ECU controls... idle and warmup question

[joeym4130]

What role does the ECU play during the warm up of the 1g DSMs? Cause I've been having an Idle problem and now was thinking about more options. Here is what happens, I sit in it to watch.
When the car is started cold, in this freezing erie weather, it idles ok, a bit high but steady. Then maybe after about 2 mins of idling ok, the rpms climb steadily higher to 2500 and sits there for maybe 40seconds. Then it drops back down to 1100 and surges between 1100-1500 once it reaches operating temp, after startupmode, the way it does the rest of the time driving. Nothing else is wrong with the vehicle, pulls great, runs right, just idles wrong.
I think some sensor is getting messed up...cause whatever mode the ECU runs in during startup/warmup the idle is steady. I have yet to put in my new MAF, maybe that could be it who knows. Just wanted to know of any other thoughts on the matter... thanks.

 

[CurtTSI]

The first thing I would do is check the resistances of the coils in the ISC servo. The connector has 2 rows of 3 pin each. The resistances between the 2 center pins and the pins on each side should be between 28 and 32 ohms. If this is not the case, that is probably your problem.

 

[joeym4130]

my ISC is good....i had a bad one, replaced it and it idles a bit better now, still surging though. Before the surge was like 1000-2000RPMs...
I am just wondering what else the ECU starts reading and trying to adjust for after warmup that can cause the surge...

 

[Thunderskull]

If your ISC is good there are a few more things you can check. The following is a really good vfaq on idle surge. http://www.dsm.org/how-tos/tttt/tttt3.html If none of these are your problem, check your ECU. An ECU with leaky capacitors can cause your funky idle. I know this from experience. This can also result in damage to your ISC and vice versa. My ISC failed and actually set the ECU on fire. The ECU that got burnt replaced one with leaky capacitors. You can have an ECU with leaky capacitors and not smell the fishy smell inside the car. The only thing to do is to pull the ECU out and remove the casing. Inspect the board. On mine I couldn't smell the fishy smell in the car, but I sure could once I opened the casing.

I hope this helps.