My wife had a high RPM incident a couple weeks ago. She has a second car and hasn’t driven the Olds much since then. She took her foot aff he accelerator but the RPMs remained high. She was able to control the car well enough to get home and stop it in the driveway. Inches away from the garage door, of course. I checked range of motion of the pedal before starting the engine and it seemed to be fine. I started the engine and it behaved normally. The Silhouette has a throttle cable and it seemed to move well, though I did not inspect it. I drove around the neighborhood and it still was fine. Since then, we haven’t driven it. I want to figure out a plan of attack to troubleshoot the issue. The main problem I see is that it is intermittent and I might not be able to find any issues. I don’t want her to drive it, and in a month we are expecting a new baby! Well, grandbaby. I don’t want her driving the newbie around either in the van until we fix it. I’d appreciate your thoughts.
Well, inspect the throttle cable, but it wouldn’t surprise me if the floor mat got jammed against the pedal, and then when she got out of the car it got shifted so that you couldn’t tell what had happened when you looked.
If the IAC valve goes to the wrong position for the idle condition, it allows too much air past the closed throttle plate when the accelerator is released. The O2 sensor detects this excess air, and the computer adds more fuel which causes the high RPM’s
I looked for that first. The pedal never touches the floor. It is pinned about 8" to a foot off the floor and the cable attaches above that. I’ll take a closer look at the cable. It is 15 years old after all. The IAC valve is 15 years old too, of course. My concern is that with an intermittent problem, fixes like the IAC valve might be throwing money at the problem. I’m not suggesting it’s the wrong diagnosis, just that I’m not sure how I’ll know it fixes the problem.
Edit: I found an electrical check in my Haynes manual. The resistance across terminals 1 & 2 should be the same as terminals 3 & 4. I’ll get my VOM out and give it a shot.
I’ve never had the experience where the engine won’t slow down enough to drive safety. But my VW Rabbit’s throttle cable would stick sometimes, so if I were going 40 and wanted to go 30 it might take 15 seconds for it to finally retreat to 30. I fixed that by removing the cable and dripping some wd40 down inside the cable, then letting it hang in a vertical orientation overnight. My Corolla’s IAC failed one time, which caused a high idle rpm, but didn’t affect high speed driving. In fixing that problem I discovered a lot of gunk on the back side of the throttle valve area which was causing it to stick. De-gunking the throttle valve fixed that problem.
As you pointed out, intermittent problems can be hard to diagnose and even harder to know if they are solved. In the interest of safety, everyone who drives this car should practice shifting into neutral while driving this car until they are confidant they can do it smoothly in an emergency.
This is the safest response to any unintended acceleration problem and everyone should be prepared to do it.