High Idle When Warm
 

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.

Re: High Idle When Warm
 

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

Re: High Idle When Warm
 

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. ;)

Re: High Idle When Warm
 

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.

Re: High Idle When Warm
 

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)

Re: High Idle When Warm
 

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


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.

Re: High Idle When Warm
 

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

Re: High Idle When Warm
 

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

Re: High Idle When Warm
 

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.

Re: High Idle When Warm
 

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?

Re: High Idle When Warm
 

Hook up a logger and see what coolant temps the ECU is seeing (gauge, rad fans, and ECU all have different sensors).

I highly doubt the ground strap on the downpipe would cause this since 99% of DSM's either now have aftermarket exhausts or the strap has corroded and broken off.

Re: High Idle When Warm
 

Ecu reports the same as the aftermarket gauge. Sorry, I didn't realize the gauge and ecu had different sensors.

Re: High Idle When Warm
 

in order to check coolant temp. sensors you need to warm them to 140 degrees F? and check for continuity, if its a open circuit it needs replacement.

This is coming from Mitchell On Demand. Auto Program from work.

Re: High Idle When Warm
 

I just finished fixing the idle on all of my friends DSMs, so you may want to listen up.

First, take that retarded block-off plate off your DSM, trust mitsubishi on this one. Un-loop that coolant hose, and put the hoses back in the stock configuration.

The FIAV is great, it causes the engine to warm up faster, so your engine will last longer. Cold pistons = piston slap. The FIAV does not cause F*cked up idle, no matter how much you want to believe it.

Your ISC is dead, you need to throw it away. It also has ruined the driver control circuitry on your ECU.

SO now you have a ruined ISC and a damaged ecu.

Second, you need to buy a new ISC from www.dsmisc.com $140

Third, you will need to send your ECU into dsmchips.com -or- the DSMLink guys so they can fix the ISC controllers. $50.

If you dont believe me, take your DSM out for a drive, get going about 30mph, let off the gas while in Nuteral. Your engine should go down to ~1000 RPM. Now press on the brakes, at a complete stop, wait 2 seconds and your car should kick down to ~750RPM. This is stock behavior for a stock working idle control system.

I learned all of this from reading VFAQ BTW.

Oh, and mitsu temp sensors work great, or your car does not turn on, there is really no in-between with them. They wont be "just a little messed up"

Re: High Idle When Warm
 

I actually replaced the ISC before installing the block off plate. I had bad resistance across one set of prongs on my old one, the replacement was fine. I've been in need of an eprom ecu though, so this may just be another excuse to fork over some cash for one.

Your opinion of a new ecu with keeping the block off plate? (aside from the general liking of the ISC function)

Re: High Idle When Warm
 

Is the Check engine light on?

Re: High Idle When Warm
 

LOL!

Re: High Idle When Warm
 

Agreed. :score001:





For real though, no codes.

Re: High Idle When Warm
 

Just curious, how does the circuitry on the ECU get damaged?

Re: High Idle When Warm
 

lots of reasons, caps can leak and mess it up...