I have an '86 Olds Calais Supreme with a 2.5 liter and a 5 speed. It has
180,000 miles on it. The car stumbles/bucks when cruising below roughly 2,000 RPM at steady throttle, not accelerating. IF I give it a little more gas it will smooth out until it has settled in at a higher speed. If I accelerate enough to bring the RPM up above 2,000-2,500 it will run smoothly.I have tried revving the engine in neutral, and get weird results. If I push the gas in a little to bring the RPM up to about 2,000 it will jump to 2,000 pretty quickly, run smooth for a second or two, then slowly drop to about
1,000 and run very rough/misfire. If I let go of the gas it drops to idle and idles pretty smoothly at 800-900 RPM (will slowly go up and down). Similar results if I give it gas to a higher RPM in neutral. It will go up to a given RPM, then start to stumble/misfire and slowly drop to about 1,000 RPM below where it initially went up to. If I give it a lot of gas in neutral to go to maybe 4,000 RPM it will stay up around 4,000 RPM and run smoothly.When I got the car about 3,000 miles ago I gave it a tune-up which consisted of oil and filter, air filter, spark plugs, spark plug wires, distributor cap and rotor. I also put a bottle of fuel injector cleaner into the gas tank and cleaned up the throttle body as best I could without removing it by using throttle body cleaner. This greatly reduced the bucking/stumbling problem it had when I first got it. It wasn't bad at all after that and would only do it occasionally at particularly low RPM. I could cruise at
1,500 RPM and have no trouble.The problem only got bad like I mentioned today after a session with my girlfriend driving, who is still in the process of learning how to drive a manual transmission, or shall I say, still learning finesse. ;) Anyway, as rush hour approached she got nervous about other cars and dragged the RPM down to 500 or so a few times before I told her to downshift, made several violent shifts, and towards the end stalled the car a lot, in a violent manner. The problem started after she stalled it three times in a row. She told me the check engine light came on. She stalled the car again seconds after that, and it didn't come on after she started the car, and hasn't come on since.
Right after that the problem got to the severity it is now. The car had all these symptoms before, but they were very minor, and I could even go a couple days without noticing any trouble. She was much harder on the car when she first started learning, and the car never gave any trouble. I don't really understand what could have happened to cause the current problem from her driving, so maybe it was just a coincidence.
Any ideas what the problem could be? All of my knowledge of cars is from my first two cars, a '67 Galaxie 500 and a '68 Galaxie 500, one had a 289 and the other a 302. I'll be driving my '68 again within a month or so when I get my new engine in, but I'm giving the Olds to my girlfriend so I would like it to be running properly. My only thoughts given my limited knowledge of modern fuel injected vehicles would be either a vacuum leak, malfunctioning IAC, malfunctioning EGR valve, malfunctioning throttle body, or dirty fuel filter. That is the order I suspect them in. Hopefully Thursday I'll have time to go through all that. Any thoughts or suggestions would be greatly appreciated. Thanks.
Cory