High idle when hot

[argiopeweb]

I'm having an issue where, after heating up via city driving, or immediately after even 10 minutes of highway speeds, the car will idle at 2.1k rpm. Easing into the clutch while on the brakes (to slow down the engine at the expense of my clutch) brings it down to proper idle speeds, but it slowly increases (over 30 seconds or so) till it hits 1.8k, then pops straight back to 2.1k rpm.

This seems to be a problem others have had, but my particular instance seems asymptomatic in two ways. First, most people having "high idle" are referring to 1.1k rpm, not my 2.1k. Second, when I turn off my engine and restart, I idle where I'm supposed to, and the problem may not come back for 1-2 stops worth of city driving.

As a result of my slightly odd symptoms, I decided to poll the community prior to ripping apart my idle control valve, throttle body, and AFM on my daily driver. Thoughts?

[rick13]

mine was the tps

[mikepellegrini]

Here's a link to Clark's manual on the TPS: Throttle Position Switch - Information, Troubleshooting, Replacement, and Adjustment

I've had problems with idle that were caused by vacuum leaks, as well. That can be diagnosed with a vacuum gauge. How to Use and Interpret a Vacuum Gauge

[PDX-944]

it seems like a far shot, but my high warm idle was due to the cruise control motor pulling on the throttle cable too much. i dont know why it occurred only when warm, but i disconnected the cruise control cable at the motor and it dropped right back down.
one thing to try, when its idling high, pull the pedal up with your foot. does it drop back down?

[mikepellegrini]

Originally Posted by PDX-944

it seems like a far shot, but my high warm idle was due to the cruise control motor pulling on the throttle cable too much. i dont know why it occurred only when warm, but i disconnected the cruise control cable at the motor and it dropped right back down.

I had that exact problem when I put a new engine in my 951 and it drove me nuts for maybe a couple months, before I finally figured it out.

[argiopeweb]

Apologies to all for not getting back to you. I've been living with the issue for the last couple of weeks. Threw a new fuel pressure regulator in yesterday and fixed a leaky vacuum line from the bottom of the J-boot (the one that goes to the ICV and brake booster), and that seems (from the little driving I've done) to have completely fixed my issue. No cruise control on this car, but if the problem pops back up I'll definitely throw a multimeter at the TPS.

Thanks all.

[FRZ951]

Is the idle problem came back?

Hi, my name is Matt, im from Quebec, Canada. Summer is coming back in few months and I wish to fix my idle problem before the summer. Ive the same issue as you had. When its hot outside, at the red light sometimes (not always) the idle raise and stay high all the red light. Sometimes the idle return to normal during the light, sometime the idle is just normal.

For some things to test such as Vaccum leak, TPS and my cruise control is disconnected.

Can be interesting if the idle still good fpr you. thanks to let me know and sorry for the poor english :P