High Idle When Warm

[xveganxcowboyx]

My car has always idled high when warm and I'm sick of it. I just got my new stroker in and want to get it reasonably tuned and drivable and this is screwing me up. Here's the pertinents:

Always idled high (especially in warm weather). This means for 2 1/2 years, from completely stock to where it is now.

Did it on stock MAF. Now does it with MAFT.

Did it with stock throttle body, cleaned, changed seals (2 years ago), changed sensors, finally installed QPR block off plate. Still does it.

This is the third engine, no change.

Did it with original cooling system, does it with aluminum radiator and slim fans (though the idle rises more if the engine temp rises above normal on either setup)

Did it with stock EGR and with QPR block off.

Did it with original vacuum lines, now does it with just Cruise line, Boost gauge, BOV, stock FPR line.

Did it with boost leaks (when I bought it), does it now with no leaks.

Did it with old O2 and replacement O2.

Did it on original fuel system and does it on EVO injectors and pump.

etc.............


The car idles fine on start-up (a little rough/low now with the TB block off) and is fine up to about 170 degrees coolant temp. Then it starts to rise. It takes 5 to 10 minutes for it to get from ~800 rpm to 2,000 or more. It's been over 3,000 rpm in the past. I can take fuel out of idle range, but then it idles too low to start properly when cold.

If it's at all helpful I've also always had a crappy voltage issue. Starts out between 13 and 14 volts, but lowers to 12-13 depending on accessory use after warm-up (follows same pattern). Not sure if it has always done this, because I haven't always had a volt gauge. Alternator is 1 year old 90 amp model.

[mnim15]

Mine does the same thing. Have you tried changing the throttle cables?

[xveganxcowboyx]

No, but I just came across a post online that said loosening the throttle cable can help (I actually just did the opposite thinking it might help). I won't have the chance to mess with the car again for a few days, but so far I've got a few things on my to do list:

Loosen throttle cable
Remove Throttle Body and inspect. Make sure the plate opens and closes easily (It did when I had it out last)
Double check the timing

Feel free to add to my list. It's obviously not one of the usual culprits so unlikely suggestions are just fine. ;)

[AwdGSX13]

since you have the block off plate, its not going to want to idle normal. At least mine doesn't it idles like shit until warm then its perfect.

*Edit*
This is assuming to removed the FIAV and IAC.

[1QUICK4]

Check your Base Idle screw and you can try adjusting the throttle body blade with the closed throttle position bolt (under the one wire harness, back side of throttle body)

[xveganxcowboyx]

since you have the block off plate, its not going to want to idle normal. At least mine doesn't it idles like shit until warm then its perfect.

*Edit*
This is assuming to removed the FIAV and IAC.

Problem existed before TB block off. It causes the rough cold start, but not the rising idle.


Check your Base Idle screw and you can try adjusting the throttle body blade with the closed throttle position bolt (under the one wire harness, back side of throttle body)

Biss has been adjusted every which way. That just shifts the idle range as it should (so I could bring cold idle from 700 rpm to 900 rpm, but once it warms up it would just go from 2000 rpm to 2200 rpm).

Can you elaborate on the closed TB blade and bolt. I'm not familiar with it. Does it just adjust like the BISS? What does it control?


*edit* Anybody know anything about the exhaust ground strap. I read that could effect the O2 operation which could in turn effect idle. My car has never had one.

[x-pride]

If you have cruise control. Adjust your cruise control cable when the car is warm.

[xveganxcowboyx]

The only real luxury I have left on the car. I'll add that to my list. Thanks.

[AwdGSX13]

what about bad coolant temp. sensors. Ive heard of this causing Rough Idle's? Dunno if you stated replacing that with the new cooling system.

[xveganxcowboyx]

No, they are original. The only thing I know is my factory gauge matches my after market one and my fans come on when the car is hot. Do you know of a way to test them?