GazzaGSi Posted October 28, 2005 Share Posted October 28, 2005 After picking my Supra up last Saturday I have started to have some strange idling problems. It was fine until Sunday night. I had gone through the drive thru at KFC and pulled up to eat my food. In doing this I had the engine off but with the keys turned over to listen to the music. This is where the problem began. Upon starting the car it idled at 4000rpm, I turned it off and on and was the same, tried blipping the throttle and it stayed at 4000rpm still. I took it for a little run and everytime I put the clutch in the revs stayed at went to 4000 rpm. With this happening it was very difficult on bends etc as when I lifted the clutch up as the car was in such a high rev range it pulled the car forward. After giving up with it and trying to check for any obvious things under the bonnet like a air leak or the throttle stuck open I phoned the AA as I didnt want to risk driving it. After a 25 minute wait the AA turned up and asked me to show him the problem, started it up and . . . it idled perfect!! tried again and it was perfect again. After explaining to him what had been happening he couldnt think of what it may of been and we left. I got home and all was fine. But now, when I first start it it doesnt hold the revs until it is abit warm (i start at 5:30 in the morning). Continued.... Link to comment Share on other sites More sharing options...
GazzaGSi Posted October 28, 2005 Author Share Posted October 28, 2005 ... continued I spoke to the previous owner to see if he had ever experienced something like this, which he hadnt but said he would look in to it for me. The following day I receive a call from him saying he had spoken to his friend at Lexus and thinks it was the following: (cant quite remember everything he said) While I was sat with the stereo on/ignition there is something built on the engine almost similar to a manual choke system. So the longer you sit there the higher the revs will gradually increase for when you start the engine up. The reason why it didnt do it when the AA came out was because I had sat so long waiting, this mechanism had time to wind back down. To stop this from happening unplug the following plug (sends me a picture with the plug labelled) as this is only usually used on the auto models. He then says wait till the came is at normal operating temp and the revs your require and unplug it. This will then remember the revs you wish to start the car up at. My question, eventually, Has this happened to anyone on here and does the above sound correct? Many thanks and sorry for the long winded post. Gareth Link to comment Share on other sites More sharing options...
Alex Posted October 28, 2005 Share Posted October 28, 2005 Idle Air Control Valve...sounds like it could have stuck open... Link to comment Share on other sites More sharing options...
jim_supra Posted October 28, 2005 Share Posted October 28, 2005 This is happening to me at the moment was gonna start a thread about it myself, weird! When the car has just been started after sitting for a while it revs fine (about 800-900rpm) Once i've given it a run my idleing speed tends to vary from anything between 1200rpm to 2000rpm. In my case i'm pretty sure what the problem is but am not sure how to rectify it. or describe it for that matter!! It has something to do with my throttle mechanism, whereby it does not return all the way back to its resting position after being revved. there is a little, I guess you would call it a valve of some sorts that slowly allows the throttle to return to its resting position. i think this is sticking so don't know if it can be fixed or i have to replace it. Link to comment Share on other sites More sharing options...
mikeyb10supra Posted October 28, 2005 Share Posted October 28, 2005 throttle cable sticking?? Link to comment Share on other sites More sharing options...
Ian C Posted October 28, 2005 Share Posted October 28, 2005 Well, that stuff about the plug and something "unwinding" sounds like horsepoo to be honest. The ECU simply pops open the idle air control valve a bit more if you: Put the car in gear (auto) Turn on the lights Put on the rear screen demister Switch on the aircon It doesn't up the idle just because you put the stereo on, unless it puts such a huge load on the alternator that it drags the idle down but technically that's just the ECU trying to keep the engine running rather than it responding to some bangin' choons. It also doesn't up the idle if you turn the steering wheel - there is a mechanical air bypass valve for this seems odd having it in there when everything else is electronic... Anyway, your idle speed is primarily controlled by the idle air control valve. This has been known to gum up and cause idling issues. A good blast of solvent like a brake cleaner can clean it out, probably best to take it off first However. There is a sort of failsafe built into the stock ECU, where it detects a runaway engine - you can emulate this by unplugging the IAC valve while the engine is idling. It will let in so much air the engine begins to race, and at about 2500rpm it should cut the fuel, the revs will drop to about 1000rpm, and it'll bring the fuel on again, and continue this cycle (it's about once cycle every 1 to 2 seconds). If it's idling at 4000rpm, are you sure that the throttle isn't sticking open? Work it a bit with the engine off and see if it's less than smooth... -Ian Link to comment Share on other sites More sharing options...
GazzaGSi Posted October 28, 2005 Author Share Posted October 28, 2005 This is the plug i was told to disconnect (labelled: plug) Link to comment Share on other sites More sharing options...
GazzaGSi Posted October 31, 2005 Author Share Posted October 31, 2005 Anyone know what the plug labelled above does? Thanks Link to comment Share on other sites More sharing options...
colsoop Posted October 31, 2005 Share Posted October 31, 2005 Its the idle speed control valve. Thats the one Ian suggested you remove and give a good clean. Link to comment Share on other sites More sharing options...
Phoenix_TT Posted October 31, 2005 Share Posted October 31, 2005 The problems posted seem to be the opposite to what happens with mine. If I leave mine for more than a hour then when I startup the revs arevery high between 1800 and 2000 rpm and it takes a good 5 mins to get down to 1000 and below. Will cleaning the IAC help in this suitation or is my problem something else ? Here is a link on MKIV.com to some info on cleaning the IAC http://www.mkiv.com/techarticles/parts/iac/index.html Link to comment Share on other sites More sharing options...
GazzaGSi Posted October 31, 2005 Author Share Posted October 31, 2005 Thanks very much for yours help guys. Link to comment Share on other sites More sharing options...
b_have Posted October 31, 2005 Share Posted October 31, 2005 However. There is a sort of failsafe built into the stock ECU, where it detects a runaway engine - you can emulate this by unplugging the IAC valve while the engine is idling. It will let in so much air the engine begins to race, and at about 2500rpm it should cut the fuel, the revs will drop to about 1000rpm, and it'll bring the fuel on again, and continue this cycle (it's about once cycle every 1 to 2 seconds). -Ian Ian, this is exactly my problem (remember? stationary/powerbrake/revs to 3500/fuelcut, bounces off fuel cut every 1-2 secs. Anyone know anymore about this system, I am sure thats whats causing this! Link to comment Share on other sites More sharing options...
Guest Rays the roof Posted November 7, 2005 Share Posted November 7, 2005 Had my throttle body polished and now my revs are stuck at 1,200. Tried replacing all the gaskets over the weekend, but b*llox, still the same problem. Took the Air intack valve off and it seems to be working ok. Start the engine with it off, (but connected) and by controlling air rate into throttle body (put finger over hole AIV goes into), you see the valve plunger go out and come back in???? Reset ECU and tried just about everything to bring revs down (to no avail). Anyone recommend a diagnostic centre in the Midlands - APART FROM THOR THAT IS!! Link to comment Share on other sites More sharing options...
Ian C Posted November 7, 2005 Share Posted November 7, 2005 Ian, this is exactly my problem (remember? stationary/powerbrake/revs to 3500/fuelcut, bounces off fuel cut every 1-2 secs. Anyone know anymore about this system, I am sure thats whats causing this! Yep, I remember that, but I can't figure out how it is connected (not saying it isn't though, it's very similar...). I assume you can rev it up out of gear and it's fine? I wonder if your off-idle switch in the TPS isn't working...? -Ian Link to comment Share on other sites More sharing options...
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