'98 Pontiac Grand Prix RPMs Issue

When I press down on the gas, it doesn’t respond like it should. It’s slow to get going and takes too long just to even get to 35 MPH; longer up a hill or any angle. If I press down harder, the RPM reader jumps up and does not make the car go faster.

Eventually it’ll “catch” (my term, for lack of a better way to word) and there will be a hard jolt with a noise, making me think of the transmission.

Now, sometimes the RPM will jump around up and down, even in idle and online info’ suggests an issue like this can be the mass air flow sensor, but so far none of the symptoms I described in the first two paragraphs appears to be related, so this on the face of it appears to be a second and separate issue, but I thought I’d mention it anyway.

I have not yet gone to an auto place to get error codes.

The transmission may be slipping.

Remove the transmission dip stick, and check the color/smell of the transmission fluid.


Looks like a cross between the first two brown ones. Didn’t really smell it because the air is blowing big time out there. Car’s been off for hours – will that affect the smell?



So, to confirm: The issue is unrelated to the apparent mass air flow sensor problem I noted?



Thank you, Tester. I’ll run codes anyway and try and smell the fluid when hte wind dies down and report back.

Remove the dip stick, get in the car out of the wind, and smell the transmission fluid.


Probably not, and once you find out the cost to rebuild the transmission, you may well decide to give up on the car.

If you have a way to force the transmission into a lower gear, try that. Might provide a clue to what’s going on. To me this sounds like you have a slipping transmission. This is a very common failure mode for automatic transmissions. If so the first thing to try is a proper transmission service. You might get lucky.

I honestly can’t tell if the fluid smells burnt.

Went to a local auto place that does free code testing and got the following:


Camshaft Position Sensor A Circuit Range/Performance (Bank 1 or single sensor)


Insufficient Coolent Temp For Closed Loop Fuel Control


Catalyst System Low Efficiency (Bank 1) [Note: Got this one twice, so I guess that’s an error unless two entries saying the exact same thing means something]

Even though no code was given, I had to replace the MAP sensor – it was literally broken in half (some idiot broke this while working on my car and didn’t tell me; NOT something I did).

I replaced the MAP sensor, since it was a piece of cake.

The auto store guy had no idea where the camshaft sensor is located and what it takes to replace it, so I skipped buying it. After all, for all I know somebody here might tell me to trying something else before doing that.

I pulled up a video on Youtube for a 2001 Pontiac Boneville and the sensor the guy pulled out looks nearly identical to mine, so I assume mine is about in the same palce – i.e., “Hard to get to” (to quote Mal from “Serenity”):

I have no idea what the coolant temp issue even means. My car had kept running hot and getting into the red and a few days ago I found out the coolant was apparently near empty. I filled it but ran out to finish the job properly (money is an issue right now; I also have two tires that have to be replaced).

Any further advice would be welcomed.

Over 180,000 miles. Another video says the camshaft issue can be multiple things, but likely the sensor, so I figured listing the miles would help make a determination.

Umm . . . you have a camshaft position sensor code, not a crankshaft position sensor code

P0125 is usually one of two things. Either your coolant level is low, thus causing an inaccurate reading. Or your thermostat is sluggish and/or stuck open

P0240 . . . I think you made a mistake when typing in the code. But there IS a code known as P0420, which is low catalytic converter efficiency detected Bank 1

How many miles on the Grand Prix . . . ?

Out of all the possibilities, the camshaft position sensor and the thermostat are not likely the root cause for your problems

But the transmission and/or catalytic converter are much higher on the list

After ruling out a plugged cat, I’d be looking real close at that transmission. Like George said, a proper transmission fluid and filter service can’t hurt at this point. But don’t get your hopes up too high

What condition is the car in overall . . . ?!

High mileage?

Well maintained?

Rusted out?

To your knowledge, has the automatic transmission fluid and filter ever been serviced . . . ?!

Note that a completely clogged and/or internally broken catalytic converter . . . which could generate a P0420 code . . . would produce some of your symptoms. A backpressure test would reveal if it’s severely plugged or not

Yeah, I didn’t type that right – camshaft is correct.

And yes, it’s P0420; my mistake.

I edited the post and added miles before you posted.

I changed the transmission fluid once since I got it in 2006.

I don’t know what you mean by overall condition.

180K . . . the transmission may have reached the end of the road, but a trans service will give you the answer soon enough

Be realistic

Has it been serviced regularly, and by the book?

Body is clean and straight, or it’s had multiple accidents?

Is it still comfortable to drive, are the seat springs poking through the upholstery

ac still blowing cold, heater working . . . these may or not be major issues, depending on your location

to sum it up . . . do you believe it’s worth fixing the car, should it actually need a transmission overhaul?

You are talking to somebody who isn’t a mechanic, so you have to tell me what you mean by that, otherwise that’s a pretty open wide field and I wouldn’t have even known what to cover.

I have only had work done when something is wrong since I got it in 2006; I have no idea if any of it was by the book.

I was rear-ended once years ago. Took it in Pontiac and they fixed it with insurance money. Backed into some lady who sneaked up on me and the trunk is out of alignment. I can’t tell you anything about it before owning it.

Maybe you’re trying to be funny, but it’s a 2006 car with nearly 183,000 miles, so obviously it’s seen better days body/inside condition. You might say the car has character. Lots and lots and lots of character.

A/C stopped working years ago. Live in Florida.

As I am poor, getting a new car and making payments, with a credit history I couldn’t even tell you about since I don’t use it, is not an option.


And your last post gave me much needed information . . . now I’ve got a bigger picture


Are you in a position to do any of the repairs, services, or tests yourself?

I’m asking because “poor” is relative. Maybe you’ve got the money and/or tools to do some of the work yourself

Do you live in an area that has smog inspections?

If not, some of these problems and fault codes can go on the back burner

I would actually say the first thing is that back pressure test . . . if the results are favorable, you can forget about the catalytic converter for now

Next is getting the automatic transmission fluid and filter service

If it improves things significantly, good news

if not, you know the transmission’s pretty much done for. Then your best option would be to install a known good junkyard transmission. The good news is that the Grand Prix had corporate cousins which probably shared the identical transmission. A decent junkyard would know what’s compatible

I can do any repairs or tests that can either be done with tools provided to customer use at the auto place or don’t require tools (like the replacing the MAP sensor I did), and of course any relevant videos online to guide me through how to do it.

I do not live in a state with smog inspections, or thankfully. They pretty much check you can do the basics here (horn works, lights work, turn signals, other little things).

By the by, I went online to see about how much the cost of a back pressure test might run me and in the search results were symptoms of a bad catalytic converter:

Sluggish engine performance (when I get going, it works; just getting going after slowing down or stopping is the problem as I posted about)

Dark exhaust smoke (none; I have white smoke. I know, I now, a symptom of some other issue)

The smell of sulfur or rotten eggs from the exhaust (I’ve yet to smell anything that made me think of rotten eggs)

Excessive heat under the vehicle (during the summer the driver’s floor board gets hot, can’t say anything else really)

Here’s a link to a back pressure tester on ebay for under $20 with free shipping


You remove an upstream oxygen sensor and insert the tester instead. There are probably tons of videos and instructions on the internet. Possibly the tool even comes with instructions

This is what you use to remove the oxygen sensor


Probably for under $60 you could buy both tools and perform the back pressure test yourself

The idle jumping around was probably due to the broken map sensor, I’m thinking. The rpm’s going up, the car not accelerating, followed by the jolt with a noise sounds a whole lot like a slipping transmission to me, I’m afraid. Especially if the noise you hear following the jolt sounds like a rubbing or grinding sound. I’ve had zero luck servicing a transmission after it’s already started slipping. It’s the only scenario in which changing the trans fluid actually seems to do more harm than good…

If you want to check and see if the cat is clogged for free, you can unscrew the pre converter oxygen sensor and go for a test drive. The exhaust will be able to escape through the hole where the sensor was. If power is restored, replace the cat.

But, I’m still thinking the trans is slipping. The only remedy for that is a rebuild or junkyard trans. Accelerating very gently might help a slipping trans last a little longer. Try and notice if the jolt happens between certain gears. If you notice the slip and subsequent jolt always happens in a certain gear, that would confirm that it’s a trans issue.

Youtube videos also suggest a dirty or potentially bad mass air flow sensor can cause the jumps, which are still present. My next step is to clean the sensor and see what happens.

I don’t hear a rubbing/grinding sound when the gear shift, it’s more like a hard thud, I mean – for a lack of a better way to describe it – like a tiny goat with horns rammed into the car. The shift is softer is I baby it; I know where about the shift changes come, so I ease up on the gas for softer shifts (working under the assumption it is the transmission, therefore I want to extend the life until I can afford to do something about it).

About where would the oxygen sensor be? On the converter itself?

It’s too late in the day to look now and with the cloudy weather and potential rain over day, I;m not sure when I’ll get a chance to check it out.