Hello all, looking for advice on an issue that has arisen in the past few days in my 1995 pontiac bonneville with 200k miles on it which has given me no issues so far but I have started to notice that when I am accelerating from a stop I get a sharp increase in rpm and a jump in speed then immediately after the rpm and speed go back to normal. This does not occur when I am driving slowly around like a parking lot when I was testing it pretty much only when I accelerate past 30 or to 40mph. Does anyone have any idea on where/what I would start checking or if this is an issue I should take into a mechanic.
Assuming it's an automatic, it sounds like your transmission is slipping on the 1-2 shift. (Or maybe the 2-3 shift, depending on where the shift points are on your trans.) Does it have enough transmission fluid?
Hello Chuck, ive just checked it and it is a little over 1 inch higher than the maximum operating level after not running for about an hour but in fairly higher temperatures if that makes a difference (90 degrees and in sun)
I should also clarify that when I said this does not occur at low speeds I misspoke, it only has little jumps at lower speeds and much less often. also I find that 5-10 minutes into driving it happens a lot less as well I think
I guess the real question is whether this surging happens when the transmission shifts gears, or is the engine just running unevenly overall? If the former you're likely looking at transmission trouble. If the latter it could be a number of things like a vacuum leak or bad sensor. (Almost anything could wrong, after all the car is 26 years old.) You should probably have a mechanic scan the car for fault codes using a Tech2.
It doesnt seem to happen when the gears shift as far as I can tell, and the engine seems to run very smoothly other than when this happens. I even have noticed maybe when I am coming to a stop there will be a rev and then back to slowing down or stopped. I will take it to a mechanic then and see what they say, although would it need to be a tech2 specifically or could a general obd2 scanner that I could get do the trick?
That car is pre-OBD2. The Tech2 is the dealer-level scan tool for GM cars made from the 1990s through the 2010s and will read all fault codes the car can generate. Most mechanics that work on GM vehicles should have a Tech2 or equivalent scanner. A good mechanic will know what to use.
I see, thank you for all the advice I will take it into a shop tomorrow have a nice night
Let us know how you make out with it!
So I just seemed to have fixed it as far as I can tell. I went to a well rated auto mechanic in my area, described the problem and left it there for a few hours. He texted me and told me that their scanner pulled no codes, and upon inspection everything seemed to be working perfectly which was a little bit disappointing in that they didnt find the culprit but hey at least it was free and at least that confirmed to me it wasnt the transmission, The only thing he said was that it was probable that it was a vacuum leak that they could not test for at their shop. I then did some research into the symptoms that seemed to be getting worse and two things I found online had the exact symptoms, a bad mass air flow sensor and water contaminated fuel. The air flow sensor was really easy to test and it did the exact same thing when I started the car with it off. So I dumped a container of heet in and filled my tank and the problem seems to have disappeared. I will go on a long drive to run through this gas then buy another bottle and fill my tank again to really make sure all the water is gone I think.