: '95 SLS Rough Idle
06-13-07, 11:56 AM
The '95 has recently developed a bit of a rough idle. There isn't any noticeable variation on the tach, but when the car is stopped in drive there is a noticeable vibration and low droning sound.
If I shift to park or neutral the sound and vibration disappear.
I thought it might be a vacuum leak as the parking brake auto release hasn't been working for a while, so I plugged that vacuum line with a golf tee but it hasn't helped with the problem.
Throttle body was recently cleaned. There are no codes. The car drives great otherwise and mileage is normal.
If it is a vacuum leak, then it is up line of the parking brake. How old are the plugs & wires? Have you cleaned the EGR valve?
06-13-07, 03:53 PM
Plugs and Wire were done recently. I haven't cleaned the EGR though, any specific advice on that?
I believe there is a "How To" in the Tech Tips section.
06-13-07, 09:16 PM
I'll give that a clean in the next few days and let you know how I make out!
06-18-07, 02:28 PM
I wasn't able to clean the EGR valve. The fuel supply and return rail are mounted on a bracket which is bolted to the top threads on the EGR retaining bolts. The would need to be disconnected as they cannot be pushed out of the way enough to give enough clearance to get the EGR out.
I'm still not sure it is related to the EGR Valve.
Here are a few more symptoms. The problem is far more pronounced with the AC on. Also if you feather the gas when stopped in traffic the problem goes away (less than 100rpms, more like 25).
I'm starting to think it could be the ISC actuator is either bad or needs to be uncalibrated.
I doubt it is the ISC motor unless you are idling very low. Clean the TB and check for a vacuum leak.
06-18-07, 07:27 PM
Throttle body was just cleaned. I don't believe there is a vacuum leak, the only one I suspected was the parking break release, which I plugged with a golf tee.
I suspected the ISC because the idle seems just a hair low with the AC on...like whatever system that is suppose to raise the idle to accommodate the AC's load on the engine isn't quite working right. The idle is fine in park, neutral and at most times with the AC off in drive. Maybe the idle speed just needs a small adjustment....
Press on the plunger with your thumb and see if it retracts. If not I would think it may have died. You are correct. It should compensate for the added A/C load.
06-20-07, 08:25 PM
It does seem to retract without resistance so now I'm not so sure. Is there a calibration procedure or way to up the idle slightly? I've adjusted the plunger out slightly and it's helped a little but not totally cured the problem.
Press on the plunger. When it fully retracts, pull the plug. RPM should drop to about 450 (may stall). Adjust plunger to throttle gap to .060. Reinstall plug.
06-20-07, 09:01 PM
So my turning the screw tonight really didn't make a difference since the ISC was still connected. The only thing I'm not clear on is the throttle gap of .060, where is that measured?
No, turning the plunger screw doesn't help as the PCM adjusts the idle, but apparently the gap needs to be within certain spec's. The gap is between the plunger and the throttle lever.
06-20-07, 09:18 PM
That may be my issue. At idle and with the engin off there the ISC plunger contacts the throttle. So I need to push the plunger all the way in, disconnect the wiring harnes, set a .060 (inch?) gap between the throttle plate and ISC plunger and reconnect it?
Sorry for so many questions, it's my mother car and I don't have a FSM.
06-20-07, 09:26 PM
So when the car is off the gap should also be .060? I'm pretty sure that the ISC plunger is in contact with the throttle when the car is off. This could be the problem then.
No, the car should be at idle when you do the procedure.