Yet Another Idle Problem

[GeneW]

I've had a low idle for a while and decided to just deal with it but now it's started to bounce around and die sometimes. When I first start it in the morning it does what it's supposed to do. Idles at 1500 and slows down as it warms up. When the Temp Guage hits 1/2 way it runs great smooth, responsive and pretty strong for a 1.8. Idles at 550 in Drive (Can't seem to do anything to change this-gave up) After about 8 miles it starts to stumble and bounce 450-600 sometimes catching itself and going to 1000 then dropping back and and stumbling again. If I go for a few blocks it acts OK again for a short time but continues this stuff again soon. It also feels like it's working harder once this starts. Could it be a vacuum leak at the HG that gets worse when it's warm? Distributor getting warm and coil failing? (slightly out of spec Primary Resistance 1.4~1.6)
Could it be the ECU? ISC works OK.

[TaLoNBLiNGBLiNG]

I would have to say ISC motor. I replaced mine and it helped for the time being, but I still have the idle issues, but not as bad. Only thing else I can think of is if the MAS is bad (giving the wrong air/fuel ratio needed).

[saturdaynight]

Idle at 1,500 rpms!:confused: Isn't the idle suposed to be at 700 rpms. I was having idle problems I boosted the idle to keep it running. I could never figure out why it idled so bad. Then about six months later my torque converter went. had it replaced and since then, my idle has been perfect. But then again, I just have an auto so it could be a totaly different issue. Just my .02.

[ginsu417]

Most likely ISC motor, but it could be a lot of things - including something as simple as the Base Idle Set Screw.

In case you haven't already noticed, DSMs (particularly 1.8s) are plagued by idle problems. I've seen a lot of people throw away ISCs when actually all they needed to do was tune thier car. Try the following before you dump the ISC.

Adjust your TPS sensor. Over time, the TPS will change values due to age. It's the black bottle cap looking one on the side of the throttle body that reads the angle of the throttle plate. There are 2 - 8mm bolts securing it. Loosening them a little, and turning it counter-clockwise will give you a leaner mixture, while turning it clockwise will give you a slightly richer mixture. I have found that the best way to nail this one is to tet the car warm up to operating temperature and turn the TPS counter-clockwise until you get a check-engine light, then back it up a few degrees at a time until it goes out. This will get you the best performance, assuming that your ignition is timed correctly.

Turn the BISS (it's the one with the phillips head, not the slotted one) until idle speed starts to increase. Unplug the ISC motor from the harness and back the BISS down until you're at the idle speed you want. Then shut the car off and plug the ISC back in. You may or may not need to Turn your air conditioning on, if you've got it, and adjust the slotted screw until your RPMs are 50-70 above your base idle. This screw doesn't just adjust your air conditioning idle adjustment, it also changes the rate at which your idle will drop when you shift. If you start to hear pings and misses while you're driving, turn the TPS a few more degrees clockwise until it goes away.

Improperly tuned vehicles will burn ISC motors much faster than properly tuned vehicles, and the idle speed is one area that most DSMers neglect to set right. Because the computer controls idle speed, most DSMers consider it "automatic" and don't bother to set the BISS (Base Idle Set Screw) and the computer idle adjustment screw to where it should be, so the ISC motor is left with the task of keeping the idle up, when the throttle plate should actually be held open most of the time by the BISS. This puts unnecessary wear on the ISC motor and eventually causes the erratic idle problems you're describing. If you replace the ISC motor, you should still tune the car's idle afterwards in the manner described, or you'll be complaining of idle problems again in no time.

- K

[GeneW]

Thanks for replies.
(ginsu417)
I've set the Idle and the TPS both more than once. Each time I did it exactly according to the instructions in the Haynes manual.
Why is your way better? Just want to know not being a jerk :)
The ISC works as it should (closes TB plate to slow,catches and raises idle most times when it stumbles, raises idle when moving)
Timing is right on (done after changing Timing Belt 2 mos. ago.
Today after it stumbled and died it stayed perfectly at 750 for about 10 stops then back to the same. ( I drive in traffic a lot)

[GeneW]

Waited too long to edit :o
(saturdaynight)
1500 when cold.
Were there any other symptoms when this happened?
Mine seems to shift funny when this stuff happens.
It acts like it's going in and out of gear when creeping along in line at a stop sign and holds second too long at easy throttle.
Any idea why TC would affect idle?