My '91 Q45 is idling way too high, please help!

[silverQ]

It is weird as my car's idle speed was fine when I got it; it had 5 injectors working properly. I replaced the worst injector and the idle speed was still fine. Then I got a good deal on some used injectors so I replaced the 4 worst. The car runs much better overall but at times the idle is crazy like 3,000 RPM in park. Sometimes it like rectifies itself and idles a normal speed; like mechanically it drops like 300 RPMs at a time from 2,000 until 800ish. It's like it's fighting me to come to a stop. 1500 RPMs is more common lately but it is still super annoying and doesn't help the brakes or gas mileage either. Many thanks for the help ..

[elwesso]

I bet someone tinkered with the IAC and it needs to be reset.. Turn it all the way in and turn it about 3 turns out... Inspect the screws on the TB to ensure no one fooled with them.... If they did, well, look at the quote in my sig..

[silverQ]

I'll try that .. one thing I noticed is that it's like the computer can't figure out how fast the car is going. When the car comes to a complete stop it's still pulling good and I take it out of gear I can hear the IAC racheting as the RPMs fall to normal; takes like 15 seconds. Something happened last time I took the plenum off, vacuum leak or something.

[Q45tech]

Why one uses a Consult or Consult like software to read the IAC duty cycle.

Since air can only get in thru the MAF or a leak after the MAF.

One must become one with the ecu so you can read all the input and output parameters to spot something wrong.

The ecu is so dumb that even a dee duh dee has 100x more computing power.

[goody90q45]

.....One must become one with the ecu so you can read all the input and output parameters to spot something wrong.

Grasshopper. Listen to the masters. Consult> IAC adjustment

[sdkhalsa]

Here is a little thought. Assuming that your car is not idleing high all of the time, at the time when it is running properly disconnect your IAC. I think that you will find that the problem goes away. This will indicate that there is a problem with the IAC or one of it's inputs. As noted in many previous posts, the IAC's need to be cleaned very meticulously every once in a while or else they can stick. You might also get a vacuum gage to make sure that there is no manifold leak($7.00 at Harbor Freight). Of course, the Consult info, is definitely the way to go.

[silverQ]

Hello giving update with a fix for the problem.

When I originally removed the plenum to replace some injectors and then

reinstalled the plenum the small coolant hose running to the idle cam assy

(uses thermal wax to control idle) was kinked causing the high

idle. All is now well ..


Modified by silverQ at 5:36 PM 9/14/2009