hanging idle, not iac

[86turbo]

hey guys, 85 coupe with mass air efi 5.0 transplant. When I come to a stop my idle will hang at 1500 then drop to about 800. This isnt a "how to set your idle" thread either, i've already gone through the procedure and it didnt fix.....im not throwing pertinent codes either. Anyway if my car is idling in the driveway and i rev it up the idle will hang at 1500 also but it does the same thing with the iac totally unplugged. Should it hang like that?

thanks,

Drew

 

[jrichker]

At this point, you have probably have mechanical problems and not computer related ones.
Since the problem will happen when you just rev the engine, here are some things to try:
1.) Disconnect the IAC.
2.) Disconnect the throttle cable and any linkage attached to the throttle.
3.) Start the car and observe the idle speed.
4.) Increase the engine speed to 2500 RPM, hold it for 5 seconds and then let it drop back to idle.
5.) Observe the idle speed: if it dropped back to the same speed it had when you first started the car, you have some throttle linkage problems.
6.) If the speed hung and did not drop back to the same speed it had when you first started the car, you have either a vacuum leak or a problem with the throttle body binding. Some throttle body cleaner may help with a sticking throttle butterfly.

 

[86turbo]

ok I did as you suggested. The idle speed hung with the iac and throttle cable disconnected....it hung at a lower rpm though, about 1100. I hooked up the pms from my other car to check the sensors, I know for a fact that the tps, ect and iat sensors are reading fine. My 02's are on the correct side and are fluctuating appropriately. Could it be my injectors? I have used injectors on there and they had been sitting for a while. I went over my entire intake system, vac tree etc with brake clean tryin to find a leak and have it flare up. For the hell of it i also replaced my vac lines, didnt change anything. The pms showed my timing is correct and that the ecu is receiving a signal from the maf which is the same voltage as i witnessed with my dvom. i tried manually controlling the iac using the pms and still couldnt get it to idle worth a ****. I even tried adjusting my base timing up and down and also the injector duty cycle, that didnt seem to help either.

I'm starting to think i may have a weak injector, wouldnt this affect wot performance because it pulls pretty hard.

Drew

 

[jrichker]

Check out the linkage and throttle butterfly before you go chasing other problems. It may be as simple as a throttle butterfly that binds as it closes.

 

[Redtallman]

could be the intake has an air leak or vacume line have a leak. had that problem sprayed carb cleaner around intake and it reved up a notch so plug the leak .also did u hook up the vss on the mass air swap.

oh didnt see u tried that well clean the mass air meter if you have and kn filter on it it may have oil residue from the filter therefore coating the hot wire and it wont read well. also what year wiring harness are u using better yet ecu .if its and 86 o2 are different,from what i read most of the time its the o2 not reading correctly,or could the water temp sensor keeping it in cold start loop

in the morning start the car listen to the engine .it should crank and run at higher idle when cold then once the water warms in the block that signals the ecu to go from cold start mode to warm mode the idle should drop then to 850 to 900 if it stays higher then its the temp sensor if it does but hangs then i would say its the o2 sensor.

had a 86 same problem went and bought wiring harness all sensor except o2 and water temp. only found the problem whe i un hook the wiring for o2 and it ran the same put new o2 in ran like a champ

then they stole it

life not fair sometime