Still Poor Cold Starting And Idling

[LAURIE MILLS]

:duh: Any ideas out there. I detailed in a previous post a persistent problem with my 97 Mk1 GS 300. I thought the problem was solved, but I suspect the percieved improvement was due to the engine being slightly warm when I started it, as when fully cold (down to ambient) the problem persists.

What happens is that when starting from cold the engine fires up fine, but will not idle at all when cold. If you keep the throttle open so it runs at over 1500 it will keep running, although there is a persistent slight misfire, and the exhaust smells of petrol, indicating unburnt fuel. Once the temperature gauge reaches over the point halfway between cold and normal the engine will idle smoothly with no problems. If you take your foot off the throttle before then the engine will die and will then be difficult to start unles syou leave it for a wheile to get totally cold again.

I took the car to Lexus Leeds last week and asked them to try to diagnose the problem, leaving it with them overnight so that they could replicate the problem, which they did next morning, but when they hooked up to the diagnostic computer it showed no faults, much to the consternation of the excellent and incredibly helpful Service Manger who was enough of a gentleman not to charge me for the diagnostic work, feeling that on priciple he could not charge me for failure, and that he did not want to "spend hours and hours at £90 an hour on a trial and error basis".

I have cleaned out the throttle body and idle air valve (helped a little), adjusted the throttle position sensor to raise the idle speed slightly (when warm now at 900 off load, 750 in gear), replaced the ecu engine coolant sensor, replaced the plugs, distributor cap, plug leads, cleaned the air mass sensor, and ran two cans of Slik 50 fuel system cleaner through the fuel system.

I am tempted to buy a throttle body from a breaker )i have been offered one complete with the IAC vallve and TPS) and either swap it out the IAC and TPS individually, or just change the whole assembly, but I would be shooting in the dark, and could find I had thrown away £150, so any ideas would be appreciated.

BTW I have had the vacuum checked, and it shows 17 bar, a bit low, but there are no apparent leaks, and it should not cause this problem anyway.

Other than this problem the car runs well, has used no oil or water over 3500 miles, and returned a close to optimal 26 mpg on a recnet 450 mile run to Glasgow and back.

Help please all you Lexus experts.