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It sounds a lot like fuel starvation to me; if you can blip it to 5k, does it drift back down to 4k even if you keep your foot planted?

Also - how does it drive up-to 4K? Pulling like a train, or is it struggling to pass ~3.5k before finally peaking at 4k? Or does it suddenly lose power & just stop accelerating? Is there any kind of juddering near the 4K limit, either under acceleration or cruising (although cruising in top @ 4K is fairly motoring...)?

Is there a secondary fuel filter which might also be blocked (had a Nissan Patrol like that - 2 fuel filters, one obvious one on the engine & one in the tank... despite replacing the (filthy) on-engine filter, it refused to do more than 50mph until the filter in the tank was cleaned; at which point, normal service resumed).

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Ok just had a thought whilst I was looking through some old computer course work I did many moons ago and came across the phrase GIGO. Garbage In Garbage Out.

I then remembered reading on a forum somewhere the USA ones I think that someone had experienced lumpy running from a faulty temp sensor being dirty.

Now since this issue is bugging me and I really want to know what the problem is, I have been trawling the USA sites and at least two people have described the same 4000rpm issue and have had complete and or partial success with cleaning a temp sensor and the other replacing a faulty water pressure cap! Can it really be that silly? Neither of them had codes suggesting probs with cooling system but if you think about it, it could make sense. The ECU might back off to avoid damage which would explain why some of us instinctively feel that there is fuel starvation going on.

A cheap fix and probably easy to check.

Another thread some where suggested alt belt wearing away at wires and causing a short but no closure or explanation on cure.

You are not alone!

It is fixable!

Dont give up!

And please will someone take over trawling the American sites, my eyes are going squiffy!!

PS Please keep us informed, I love a success story.

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The latest is that the Lexus dealer is stumped and can only suggest coking up of the engine, which to clear, would obviously mean more money, which I can't justify.

Thanks Guys, I'm going to settle up with the Lexus dealer then bring it home and try as many of the things you have suggested as I can. It's a pity this can't be fixed or at least diagnosed.

One of the problems I have is that I have hardly any time at home so tinkering is not really an option but I will try as much as I can.

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It sounds a lot like fuel starvation to me; if you can blip it to 5k, does it drift back down to 4k even if you keep your foot planted?

Also - how does it drive up-to 4K? Pulling like a train, or is it struggling to pass ~3.5k before finally peaking at 4k? Or does it suddenly lose power & just stop accelerating? Is there any kind of juddering near the 4K limit, either under acceleration or cruising (although cruising in top @ 4K is fairly motoring...)?

Is there a secondary fuel filter which might also be blocked (had a Nissan Patrol like that - 2 fuel filters, one obvious one on the engine & one in the tank... despite replacing the (filthy) on-engine filter, it refused to do more than 50mph until the filter in the tank was cleaned; at which point, normal service resumed).

Thanks AdeV, It seems to be a fairly fixed limit, apart from the time I blipped it and got 5000, no juddering, ever. It pulls OK to 4000 but when I get it back I can try to offer more info.

The fuel filter near the rear had been replaced.

I'm not so sure about fuel starvation as I have had it up to quite a speed where it must be using quite a bit of fuel and probably more fuel flow than 4000 at standstill.

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Haven't read every single post on this, so if youv'e tried this sorry to repeat it.

Did you check that when you floor the accelerator, that the throttle really opens to its fullest

amount? i.e wide open

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Haven't read every single post on this, so if youv'e tried this sorry to repeat it.

Did you check that when you floor the accelerator, that the throttle really opens to its fullest

amount? i.e wide open

Not 100% sure if this has been checked but it senses enough demand to kickdown when you are moving and the first garage did check the throttle position

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Ok just had a thought whilst I was looking through some old computer course work I did many moons ago and came across the phrase GIGO. Garbage In Garbage Out.

I then remembered reading on a forum somewhere the USA ones I think that someone had experienced lumpy running from a faulty temp sensor being dirty.

Now since this issue is bugging me and I really want to know what the problem is, I have been trawling the USA sites and at least two people have described the same 4000rpm issue and have had complete and or partial success with cleaning a temp sensor and the other replacing a faulty water pressure cap! Can it really be that silly? Neither of them had codes suggesting probs with cooling system but if you think about it, it could make sense. The ECU might back off to avoid damage which would explain why some of us instinctively feel that there is fuel starvation going on.

A cheap fix and probably easy to check.

Another thread some where suggested alt belt wearing away at wires and causing a short but no closure or explanation on cure.

You are not alone!

It is fixable!

Dont give up!

And please will someone take over trawling the American sites, my eyes are going squiffy!!

PS Please keep us informed, I love a success story.

Hi abs 66

I would agree to some extent with your theory on the sensors but I think according to the troubleshooting section on the engine these would show as fault codes,The theory could be extended to my theory that the ECU is faulty and is assuming these faults ,the thing that will baffle the techs is that as the ECU itself as no fault code when faulty we can't determine it is ECU that is faulty unless we try another one.

This post is starting to sound like a situation comedy starring John Cleese, Si!

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Hi,

Just looking at the matrix chart for the '91, most of which should still apply (although you've eliminated most of it)...

For "Hesitation/Poor acceleration" it lists:

Ignition Signal Circuit, Main Oxygen Sensor Circuit, Water Temp Sensor Circuit, Intake Air Temp Sensor Circuit, Air Flow Meter Circuit, Throttle Position Sensor Circuit, EGR System, Injector Circuit, Cold Start Injector Circuit, Fuel System Circuit, Fuel Quality, Vacuum Leakage, Spark Plug, Ignition Coil, Distributor, Accelerator Pedal Link, Brakes drag when released, Sub Throttle Valve faulty, ECT faulty, Engine Mechanical & Others, Engine & ECT ECU.

It then suggests:

Valve Timing, Timing Belt, Piston Ring.

Well, you can cross off 80% of that lot, and just a thought - has there been any work done on the transmission? If somebody forgot to reconnect a plug somewhere, it might think it's in a low gear which will also limit the RPM.

Thanks CD, do the above produce fault codes? If so then the top paragraph can be eliminated, the Lexus dealer is sure the timing belt is OK. Pretty sure its not the brakes.

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Plugs, HT Leads, Dis. caps and Rotors all changed and the problem is still there. If I can't get this fixed in the next week, it's going to the scrapyard.

None of this will fix your rev problem

MAF meter all the way. Faulty when under load of the throttle. This problem will not show up in any garage which include lexus dealer unless they go out on the road with a laptop inside the car while driving full stop.

Just a quick second thought what work if any was carried out before the fault or did it just happen overnight while driving?

Also don't scrap, I'll have it with the problem if car is in ok condition.

Baz.

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OK, I'm going to start a list of things to check that may not have been looked at. Before I settle with the Lexus dealer I will obtain a list of exactly what has been checked.

To Check:

Battery off for 30 mins (can pulling the ECU fuse achieve the same?)

Gearbox shift position sensor (don't actually know where this is)

Remove air filter

MAF Sensor (again), will the car run without it? and is it possible to short wires out to trick it into a false reading?

ECU: How easy is this to change?

A temp sensor

Faulty water pressure cap

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Plugs, HT Leads, Dis. caps and Rotors all changed and the problem is still there. If I can't get this fixed in the next week, it's going to the scrapyard.

None of this will fix your rev problem

MAF meter all the way. Faulty when under load of the throttle. This problem will not show up in any garage which include lexus dealer unless they go out on the road with a laptop inside the car while driving full stop.

Just a quick second thought what work if any was carried out before the fault or did it just happen overnight while driving?

Also don't scrap, I'll have it with the problem if car is in ok condition.

Baz.

I bought the car for £884 and it has had the fault since then, the first garage suspected the MAF... But the next one I put on changed nothing.

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OK, I'm going to start a list of things to check that may not have been looked at. Before I settle with the Lexus dealer I will obtain a list of exactly what has been checked.

To Check:

Battery off for 30 mins (can pulling the ECU fuse achieve the same?)

Gearbox shift position sensor (don't actually know where this is)

Remove air filter

MAF Sensor (again), will the car run without it? and is it possible to short wires out to trick it into a false reading?

ECU: How easy is this to change?

A temp sensor

Faulty water pressure cap

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OK, I'm going to start a list of things to check that may not have been looked at. Before I settle with the Lexus dealer I will obtain a list of exactly what has been checked.

To Check:

Battery off for 30 mins (can pulling the ECU fuse achieve the same?)

Gearbox shift position sensor (don't actually know where this is)

Remove air filter

MAF Sensor (again), will the car run without it? and is it possible to short wires out to trick it into a false reading?

ECU: How easy is this to change?

A temp sensor

Faulty water pressure cap

Hi with regard to the changing of Engine ECU

It is not hard to change, it is under the passenger side front console and is accessed footwell upwards behind the lowest panel of the console, the panel is removed by screws located in that immediate area. On the ECU which is a flat box approx 15cm X 10cm X3cm there are four plugs to the back and one to each side ,these are relays. the ecu plugs only go in there respective sockets so can't be mixed up when reconnecting, they have pressure release clips on the plugs so they don't just pull out, after you have unplugged one of them you will have learned the process for the rest.Make sure you dissconect the Battery before removing the ECU and dont start work for at least 5 minutes after dissconecting the Battery.

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It sounds a lot like fuel starvation to me; if you can blip it to 5k, does it drift back down to 4k even if you keep your foot planted?

Also - how does it drive up-to 4K? Pulling like a train, or is it struggling to pass ~3.5k before finally peaking at 4k? Or does it suddenly lose power & just stop accelerating? Is there any kind of juddering near the 4K limit, either under acceleration or cruising (although cruising in top @ 4K is fairly motoring...)?

Is there a secondary fuel filter which might also be blocked (had a Nissan Patrol like that - 2 fuel filters, one obvious one on the engine & one in the tank... despite replacing the (filthy) on-engine filter, it refused to do more than 50mph until the filter in the tank was cleaned; at which point, normal service resumed).

Thanks AdeV, It seems to be a fairly fixed limit, apart from the time I blipped it and got 5000, no juddering, ever. It pulls OK to 4000 but when I get it back I can try to offer more info.

The fuel filter near the rear had been replaced.

I'm not so sure about fuel starvation as I have had it up to quite a speed where it must be using quite a bit of fuel and probably more fuel flow than 4000 at standstill.

On the basis of that, yes, I'd rule out fuel starvation too. It sounds a lot like you're hitting a programmed rev limit - which to me would suggest either an ECU fault (memory corruption), or it's in some kind of limp mode. The latter seems unlikely - Lexus ought to know what limp mode(s) exist in their own ECU - but to rule it out for sure you need to do the "Battery off for 30 mins" thing to make sure its reset; although to be absolutely sure, I'd want to take the Battery off & leave it at least 8 hours - my radio settings survived the last Battery off & that was longer than 1/2 hour...

As for will the car run without a MAF? I doubt it; and even if you did get it to start, you'd not get any realistic information because trying to manually balance the air input vs. fuel input without any kind of feedback would, I think, be impossible... However, caveat: I've not tried it, so I could be talking pish...

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Hi Mudguts, I think you are right to eliminate things one by one. "when you have eliminated the impossible, whatever remains, however improbable, must be the truth" Good old Sherlock.

I reckon I would start with the Battery off as it just makes sense as you can look at other stuff while its off and if that works then its likely at some point something somewhere in all those sensors has told the ECU there is a problem. If the problem reoccurs after initially working, then either the ECU is faulty or something somewhere is telling it again that there is a problem.

I'm really sorry if I'm coming across as a knobhead but I'm really am trying to help I'm just naff at typing it out lol.

Adev has a really good point about leaving the Battery off for as long as you can as electronics can have a memory effect quite some time after power has been removed.

One of the things I ALWAYS do when weird stuff is going on in a car or computer is check then double check and clean as many connectors as I can as this is a weak point in any loom you will be surprised just how many times that works all for the cost of a little effort and a tin of contact cleaner.

The reason I brought up the experience of those people in the USA is that they described the exact same problem you have and neither of them had any codes suggesting a problem except o2 sensors which after replacing had bugger all effect on the actual problem.

They both had a problem with the cooling system one a dirty connector (see what I mean) which wasnt even faulty and the other had expansion tank pressure cap with a perished seal! If the smart arse electronics sense these probs it is feasible that it may dial down the revs almost giving a feeling of lack of fuel after 4000 rpm.

No i dont understand why no codes show but that doesnt mean it isnt doing it. Programmers can only program into a system what they can realistically expect could go wrong, so it is possible they missed this on these models and hence no code but the ECU does know somethings wrong but just doesnt know what it is. I hope Im making sense.

I think you are going to have to think outside the box on this one.

Just one more thing, are you absolutely sure your replacement MAF was OK? Baz has a point about the MAF.

Anyway good luck.

PS If you remove the air filter to test dont forget to put it back in unlike someone I know.....Ahem :whistling:

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Ok Gents I have picked the car up today from the Lexus dealer.

The following things have been done:

Exhaust & Catalytic Converters checked

Valve timing checked

EGR valve cleaned & checked

Throttle Body & Plenum Chamber cleaned

Distributor Caps, Rotor Arms & HT Leads replaced (Old Spark plugs were not suspect so replaced after new ones tried)

Engine sensor connections checked

On the way back I stopped in a layby and tried revving it up:

If you build up the revs gently it seems to get to the redline now and blipping the throttle achieves the same but (and here is the symptom that hopefully will enlighten someone): If you floor the throttle the revs immediately drop to 4000 RPM for as long as you hold your foot to the floor. If you then release it the revs will rise right up again.

Also if you play about with the throttle the engine sort of surges...

Any suggestions welcome

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After checking all from the above posts,if no better, try a fuel line pressure check...

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Look mate I'm telling you in all my years with motor car and motorsport experience its the MAF meter or MAF meter related.

When you put your foot to the floor the ecu is not getting the information into the ecu and not correcting the air mixture to burn the fuel and give you power.

These things you should do.

A) Change to a different MAF meter.

Problem still there Yes then goto B.

B) Check wiring on the MAF connector and then check there's no break through wiring to the ECU coinnector.

If all good then goto C.

C) Check there has never been water damage in car as the ecu gets white corrosion on the connector to the green mother board. Resolder connections if required.

If problem still there goto D.

Change ECU.

If problem still there goto E.

Get Auto Electrician to check the wiring to MAF and voltage to ecu when preesing throttle.

This should then show you the fault.

Baz.

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Look mate I'm telling you in all my years with motor car and motorsport experience its the MAF meter or MAF meter related.

When you put your foot to the floor the ecu is not getting the information into the ecu and not correcting the air mixture to burn the fuel and give you power.

These things you should do.

A) Change to a different MAF meter.

Problem still there Yes then goto B.

B) Check wiring on the MAF connector and then check there's no break through wiring to the ECU coinnector.

If all good then goto C.

C) Check there has never been water damage in car as the ecu gets white corrosion on the connector to the green mother board. Resolder connections if required.

If problem still there goto D.

Change ECU.

If problem still there goto E.

Get Auto Electrician to check the wiring to MAF and voltage to ecu when preesing throttle.

This should then show you the fault.

Baz.

Thanks Baz, I'll check the MAF connector again and wiring as far a I can, I'll have a look at the ECU also. I can have a look at these tomorrow.

The D and E I'll try when I'm next off from work. It could be a while before I get a chance.

Thanks again.

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Ok just before I go to bed (was up at 0400) here is the latest list of things to check / already checked:

Exhaust & Catalytic Converters checked

Valve timing checked

EGR valve cleaned & checked

Throttle Body & Plenum Chamber cleaned

Distributor Caps, Rotor Arms & HT Leads replaced (Old Spark plugs were not suspect so replaced after new ones tried)

Engine sensor connections checked

Gearbox shift position sensor (confident this isn't at fault)

Fault code 21 cleared with new oxy sensor

Throttle position sensor checked

MAF Sensor unpugged: Check engine light is on, engine runs rough and won't rev up much

Battery off for 30+ mins: Was disconnected at the dealers

Just done a check on fuel consumption after filling up: 75% motorway and the rest in town: 25 MPG

To Check:

Remove air filter

MAF Sensor

ECU

A temp sensor

Faulty water pressure cap

Edited by MUDGUTS

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Any luck yet Mudguts? Fingers crossed for you.

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Any luck yet Mudguts? Fingers crossed for you.

It's booked in with a 1UZ-FE specialist for the 20th of this month. As bazgtr says, it's most likely to be MAF or ECU related. I have done fairly large (300 Mile) trips recently and apart from this issue it has performed very well, with around 30-32 MPG on these.

I'll keep everyone posted.

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His the latest list of things to check / already checked:

Exhaust & Catalytic Converters checked

Valve timing checked

EGR valve cleaned & checked

Throttle Body & Plenum Chamber cleaned

Distributor Caps, Rotor Arms & HT Leads replaced (Old Spark plugs were not suspect so replaced after new ones tried)

Engine sensor connections checked

Gearbox shift position sensor (confident this isn't at fault)

Fault code 21 cleared with new oxy sensor

Throttle position sensor checked

MAF Sensor unpugged: Check engine light is on, engine runs rough and won't rev up much

Battery off for 30+ mins: Was disconnected at the dealers

Air Filter replaced

To Check:

MAF Sensor

ECU

A temp sensor

Faulty water pressure cap

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...Well it's with a 1UZ-FE specialist now, so far they have discovered a host of fault codes, most seem to have been related to stuff previous techs may have been touching. (When it left garage #1 they assured me it had no fault codes), these have all been cleared but one required the fitting of another O2 sensor. This could have been as the wrong sensor was replaced at garage #1. In any case it hasn't made any difference. Should know more tomorrow.

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For those still following this saga:

The latest is that the techs are down to an ECU issue or some kind of fault with the gearbox and kick-down switch / sensor / wiring.

The updated list is below of things already checked / to check:

Already checked:

Exhaust & Catalytic Converters checked

Valve timing checked

EGR valve cleaned & checked

Throttle Body & Plenum Chamber cleaned

Distributor Caps, Rotor Arms & HT Leads replaced (Old Spark plugs were not suspect so replaced after new ones tried)

Engine sensor connections checked

Gearbox shift position sensor (confident this isn't at fault)

Fault code 21 cleared with new Oxy Sensor

Fault code 28 cleared with new Oxy Sensor

Throttle position sensor checked

MAF Sensor unpugged: Check engine light is on, engine runs rough and won't rev up much

Battery off for 30+ mins: Was disconnected at the dealers

Air Filter replaced

MAF Sensor (another one tried), this would be the third on the car

A temp sensor or faulty water pressure cap (I'll discount these as just about everything like this has been checked now)

Coil Packs

To Check:

ECU

A new theory: Some kind of fault with the gearbox and kick-down switch / sensor / wiring

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