I have a 1997 Saturn SL1 with 100k. Every so often the RPMs will drop by 500-1000 or so for a second and then come back up to normal. This happens both when stopped at a light and while accelerating, and doesn’t seem to happen predictably. I’ve already changed the filters and cleaned out the IAC, without any success. I’ve sprayed the obvious connection points in hopes of locating a potential vacuum leak, also without any luck.
Any suggestions? Or are the other ways to locate a potential vacuum leak that wouldn’t be overly time-intensive?
The EGR might be clogged partially rather than a vacuum leak. Buy an EGR gasket then pull the EGR valve off (2 bolts right under the valve) and clean out the passage in the engine with a coat hanger and a shop vac. You should check that the valve itself is opening by attaching the vacuum line from the valve while its off to a vacuum source (running engine or a handheld pump) to see that it opens. These engines had issues with clogged EGR passages. Good Luck
BTW, It is idle, not idol, but your spell checker likely wouldn’t know that
I re-read your post… 500 to 1000 rpm drop? Do you really feel the drop? If not, the tach sounds like its failing. If you feel this big drop it may be an the coil pack going bad.
I thought that the EGR valve suggestion was a good one. If it is sticky and not closing all the way or whatever then it can easily account for a 500 rpm drop - or more. They can stall the car.
I would also suggest to spray around the entire intake manifold as those cars are known for gasket problems.
Vacuum leaks that come and go like that are unusual and would usually result from a faulty device like a problematic brake booster or a power steering pump vacuum valve. You’d notice the problem tracks with pressing on the brake pedal or turning the steering wheel. Or something else that is solenoid activated and supposed to affect idle speed, like turning on the AC.
Edit: Unless this engine has an idle speed adjustment screw which has been adjusted to correct a problem that shouldn’t be corrected with the idle adjustment screw. Doing so can cause the idle speed to be unstable.
Since you aren’t noticing any correspondence like that, the EGR advice above is a good place to start. When I’m testing the EGR on my Corolla, the first thing I do is make sure when I activate the EGR with a hand held vacuum pump it stalls the engine.
There’s a chance this is spark or fuel related too. A mechanic could rig up a fuel pressure gauge on the fuel rail and watch it as the car was driven. If the pressure drops at the same time the idle speed drops, that would indicate a fuel pressure problem. Doing the above is best left to a pro.
If you want to do something yourself that doesn’t take much time, you could inspect the vacuum line which goes to the fuel pressure regulator. Are there any signs of gasoline making it into that line? If so, the fuel pressure regulator likely needs replacement.
It would also be wise to have all the ECM diagnostic codes read.
Normal idle speed for this engine is 750 rpm so how high is your idle? If it is 950 or higher, you may have a vacuum leak around the #1 port of the intake manifold gasket at the top outboard corner. There is no bolt at that location because of the power steering pump and that is where the gasket fails.
Spray something on this area and if the idle changes, the gasket is bad.
The fact that the problem occurs while accelerating rules out idle controls and vacuum leaks. Investigate any fault codes that turn on the engine light. Investigate fuel pressure fluctuation.
I remember when these cars were popular we installed a lot of coils and ignition modules for various reasons.
