High idle

[Devin]

This seems to be a common problem for many different reasons. When I start my car cold it idles around 1200. If I disconnect the IAC it will hit about 1000, which is still too high. After warming it up it idles around 1500. If I come up to a light and press the clutch in the idle will dive to about 1200 go to 1800, then back to 1200 and back up again until I slow down almost to a stop.

How do I eliminate the IAC as a culprit? How do I check for vacuum leaks? What is the name and function of the little vacuum canister that connects to the IAC housing on the intake?

Thanks for your help. This is murdering my gas mileage. :thankyou:

 

[1995SHO9]

For vacume leaks you can spray break clean around all of the places where you think it might be leaking while the car is running. If it stumbles, you found your leak.

 

[itwonder]

It is unlikely the high idle is the culprit for poor gas mileage. The idle speed is computer controlled. If somebody messed with the throttle plate stop screw on the throttle body, then you may need to redo the base idle, procedure in FSM. Otherwise, try following the idle reset procedure: disco battery, lights on for 30 secs then off, reconnect battery. Start motor and turn on headlights and A/C immediately. Wait 5 min while computer recalculates idle profile. The cannister on the rear intake runner is part of the vacuum system that operates the secondary runners; nothing to do with idle.

 

[Devin]

Not that can, the little cylinder with the two connectors on it in sort of a T fashion located between the engine and the radiator.

I've performed the idle reset 4 times and it has done nothing.

It's not just the idle though, the RPMs are up period. The car pulls too much in gear, and not to mention the wacky idle fluctuations during slow downs with the clutch in.

 

[Troywakeling]

Sounds like were having the same problem. Mine will idle at like 2500-3000 after startup then I can hear the IAC kickin and drop it down to 1500 and it stays there, If I rev it up any and let off it will only go back down to 2500. Im getting a code 551 which most say is IAC circuit. I just put a new IAC on and it didnt fix it. Phoenix SHO website says code 551 is the intake manifold runner control solenoid which is what you are talking about on the back of the manifold. So im going to try to relearn the idle first. But ive also ordered the IMRC solenoid, you can get them on ebay for 10 dollars. When I hit 4k rpm im not hearing the runners kick in so maybe this will fix it or I have vacuum leaks but ive replaced most of the lines with new line.

 

[Devin]

Okay guys, here's a good one for you, what's wrong (engine related) in this picture?

 

[Devin]

Come on, no one can figure this out? Fine. It has to do with the intake.

 

[Mr Anonymous]

The missing PCV hose from the front valve cover to the intake would cause an uncontrollable idle problem.

FWIW, when you unplug the IAC valve, the solenoid will close and the car should stall. If it doesn't, you either have a faulty valve, or a vacuum leak which provides enough air to keep the engine idling.

 

[SASHO91]

What do I win????


IAC is back-ass-wards. :woohoo:

 

[Mr Anonymous]

What do I win????

IAC is back-ass-wards. :woohoo:

:laugh_ti: Indeed it is. Good catch!

How the **** does that even happen!?!?

 

[SHO_DOODmorrris]

ditto, though i would be first, yeah the line from the TB to the valve cover is off and the IAC is backwartds.. and yes how does that happen?

-Mitch

 

[SHO_DOODmorrris]

P.S yeah when i start my enigne (wether its 30 C above or 30 C below, it will start and idle at like 2500 and sloooowly go down and it sounds notchy when it does. it sits at like 1500 for a bit then it drops to about 1000 and it idles there... newer IAC already on it and that solved a problem we had about a year or 2 back when it was idling at about 3000 at stop lights so we replaced it and it went back down but for like forever it has idles at about 1000. any ideas?

-M

 

[Devin]

Josh won! Just in case you all want to know, the IAC fits either way, unfortunately! Though the harness is really hard to get on... anyway, I went reading through the SHO book and looked at the engine in the picture and lo and behold it struck me. I had the IAC on backwards! I turned it around, reset the idle and it idles between 900-1000 now. Magic!

Honorable mentions to Mr. Anonymous for catching the PCV hose missing. To answer the "how the **** does that happen", my answer is...

Now, to follow up on my question, that silver hose running from the surge tank down the left side of the engine goes to a little cylinder with another hose going off of it to the vacuum canister in the fender. What is that little cylinder for?

 

[SASHO91]

That is the line for the charcoal canister. The little cylinder is the purge valve. The CC collects all of the fuel vapor that comes from the tank, then at a certain point (noted in the EEC) the purge valve opens and releases the extra vapors back into the motor.