FAQ: Hesitation, Stutter(Studder), Shudder, Stumbling, on Acceleration/Load

I just cleaned the MAF about a week ago and put a fuel injector cleaner in the gas a little while ago. TB cleaning will probably be the next on my list. I also replaced the plugs about 4 months ago and I have driven the car maybe about 1 of those four months.

I may as well order the AC Delco wires. I'm sick of being frustrated with the thing!

Or wait a little while longer and order the Magnacor's direct from them.
I did and am very glad i did it. They shipped extremely quick and these are the best set of wires, manufacturing wise, that i have ever bought for my car.
The AC Delco's just didn't last long enough. And would break easily while doing a spark plug change, even with lubricating the ends with Dielectric.
I've had the Magnacor's on for quite a while with no issues and they are warrantied for life.
So even if you should have a single wire go bad they will ship you a new one. They are even cut to length perfectly so they fit without a bunch of extra wire or short wires.
The 8mm or 8.5 mm are not that expensive when you consider they are a lifetime wire and are built better than most of all the others. You'll be able to remove these in the future to replace plugs without worrying that the ends will break off or crack. Just remember to use a little Dielectric on the ends where they contact both the spark plugs and the coil towers.

I found the P/N and price on their website then called them directly to order over the phone. As I said i received them in a couple of days.

Zach, your problem is actually a little different from the OP's. His hesitation would occur whenever in boost (a 0-60 run at WOT definately counts here).

You say there's no problem from 0-60 as long as you keep your foot down. What happens if you don't keep on the gas?

How long have you noticed the problem? Did it come on all of a sudden? When it hesitates, do you feel pulsation, or just lack of power?

Whatever the case, you should install new wires at 140k miles as part maintenance, whether it be the problem or not. Maybe start there and see if the problem goes away.

Zach, is this problem with your '95 or '98?

It could be a vacuum leak, the vacuum line/tee is known for cracking and that would cause false MAP sensor readings as well as a funkily operating BBV, both of which could contribute to the issue.

Rick, I looked up the Magnecor model last night and the price isn't bad considering the merchandise. I honestly would rather purchase those than purchase the AC Delco's, but I'll decide soon. I probably won't be able to work on it for another month anyway, as I'll be at school.

AA, if I let off the gas going from a stop at all, then reapply pressure, the tach surges and I feel the engine kind of revving back and forth. I looked at the tach when it did it today a few hours ago and it was between 1800 and 2000. I've actually noticed the problem for maybe 1.5 years. When it happened, it didn't seem to happen all of a sudden.

Deekster, it's a prob. with the 98. So far, the 95 has been problem free. It's funny you mention the vacuum line because now that I look, there are two vacuum lines going to (forgive my laughable ignorance) a black cylindrical thing above the right side of the supercharger. I don't know what it is, but they are visibly cracked. Maybe I will start there.

I think you will find you want to get a complete vacuum line assembly, it's only available from the dealer, and comes with all the soft rubber T fittings that are probably all dried, brittle and cracked. It's a pretty common issue and not very expensive. It's the hard vacuum line that goes from the BBV (that black cylidrical thing on the right) - Boost Bypass Valve, with all the soft T fittings.

Quote :

I looked at the tach when it did it today a few hours ago and it was between 1800 and 2000. I've actually noticed the problem for maybe 1.5 years. When it happened, it didn't seem to happen all of a sudden.

I'm wondering if this is the TC clutch applying and releasing overdrive (normal). I never noticed mine for a long time, but as I started modding and changing my driving style to more spirited, I began to notice it more. If it only happens in 3rd or 4th gear, this is a possibility. If it happens in 1st or 2nd, it can't be the TCC.

I'd start with repairing the vaccum hoses, then replace the wires (nothing wrong with AC/Delphi wires, they're only $35, and they lasted you this long).

Awesome. Thanks for the suggestion, Derek. A few of the vacuum hoses are hard. Not all of them are, but some are. I will probably order the kit tomorrow. We may get 1 to two feet of snow here tonight but I will get it done. Down the road when I'm back at home for a while, I'll get the wires too even if the hoses solve the issue.

Thanks for the help, guys!

Hi,
My '97 Riviera has 147K miles. In the last couple of months, sometimes when accelerating from a stop, the car feels like the engine cuts off or the transmission doesn't engage for a fraction of a second. It only does it at the very beginning of the acceleration (under 5-10MPH). It may go for weeks without happening, or it may do it twice in one day. Other than that, it runs and shifts perfectly. I'm even wondering if I have water in the gas tank. Fluid is at the correct level and looks good. Any ideas?
Thanks,
Mikel

My initial guess is your crank position sensor is flaking out.
Has the car ever cut off at a stop light?
How old are the plugs and wires?
How does the trans fluid look and smell?

Matt

Mr.Riviera wrote:

My initial guess is your crank position sensor is flaking out.
Has the car ever cut off at a stop light?

No, but one time I couldn't start it, acting as if it had been flooded. Finally started with the gas at WOT. Ran fine ever since.

Quote :

How old are the plugs and wires?

They came with the car, but they externally look pretty new.

Quote :

How does the trans fluid look and smell?

Looks nice and red and doesn't smell burned. But I'm a manual tranny kind of guy

Thank you.
Mikel

does it seem to do it more when hot or cold or anytime?

as for the plugs/wires. are there any names on them? packard maybe? acdelco?

Mr.Riviera wrote:

does it seem to do it more when hot or cold or anytime?

as for the plugs/wires. are there any names on them? packard maybe? acdelco?

I think it's mostly when warm. I'll check the plug/wire manufacturers. Thanks.

Mr.Riviera wrote:

My initial guess is your crank position sensor is flaking out.
Has the car ever cut off at a stop light?
How old are the plugs and wires?
How does the trans fluid look and smell?

Matt

I had a crank sensor quit, is behaved like that. They are not *that* hard to replace but if you're not happy about removing/replacing the harmonic balancer (it's pretty easy with a puller) have a mechanic do it, it'll run $100 to $150 all in. The sensor itself is $30 to $50. Don't cheap out on the sensor - get a delco or delphi - in my experience (personal and observation) the cheap ones crap out again in a couple years.

Albertj

I had issues with my pressure control solenoid and the car acted as you describe. I found that manually shifting into '1' raised the line pressure enough to stop the shudder at start of moving. The real problem, however, required replacing the Pressure Control Solenoid. This happened to me at 50K miles, you are at 150K miles, probably in for a full overhaul at this point unless it's been done before.

deekster_caddy wrote:

I had issues with my pressure control solenoid and the car acted as you describe. I found that manually shifting into '1' raised the line pressure enough to stop the shudder at start of moving. The real problem, however, required replacing the Pressure Control Solenoid. This happened to me at 50K miles, you are at 150K miles, probably in for a full overhaul at this point unless it's been done before.

This is a good point too but does not explain the no-start.

Possibly/probably both are a problem (crank sensor, pressure control solenoid) given the mileage and age.

Albertj

Mike, at 147k miles, your original ignition wires need changed, even if they look new. While you're at it, check the plugs and replace if needed. OEM wires can be ordered for about $35 online.

Your problem does not seem transmission related, imo. I would do the wires first to rule that out, and then proceed to replacing more expensive and complex components.

Update:

Finally got the chance to get home this weekend. I worked on trying to figure out this problem a bit more. I called my mechanic about the wires and vacuum lines. We looked at them and he says that he had replaced them a year ago, which I had forgotten.

He also thinks that the small hairline cracks in the vacuum lines aren't a big enough deal to cause the problem I'm having. The way the tach needle swings when I try to accelerate made him think that I may need the transition to be serviced.

I'll probably get that done. Unless anybody else has any other suggestions? My car is still having the same problems that I had mentioned.

ZEP wrote:

Update:

Finally got the chance to get home this weekend. I worked on trying to figure out this problem a bit more. I called my mechanic about the wires and vacuum lines. We looked at them and he says that he had replaced them a year ago, which I had forgotten.

He also thinks that the small hairline cracks in the vacuum lines aren't a big enough deal to cause the problem I'm having. The way the tach needle swings when I try to accelerate made him think that I may need the transition to be serviced.

I'll probably get that done. Unless anybody else has any other suggestions? My car is still having the same problems that I had mentioned.

Your car is having the same problems that you mentioned. Could you recap the advice you got and list what you have or have not followed up on?

Albertj

Well, the advice I got is outlined in the post I just made. He asked me if I ever have had my transmission serviced, because he said like it seemed almost like it was the transmission causing my tach to swing back and forth. I said I hadn't, and he said that he would suggest I do that first.

With regards to following up on things, I mentioned that in the post as well. I was going to replace the vacuum lines, but the mechanic said that the small cracks were not enough, in his opinion, to cause the issue that I am having because they seem to small and not very significant. With regard to wires, he said that they were replaced about a year ago if even, so not too many miles ago, and he believed that the wires would thus not be the problem.

I also replaced my spark plugs about 3 months ago. I still feel like I want to do at least the vacuum hoses first, as they are cracked somewhat, but the fella thought it wouldn't be the problem so

OK.

Vacuum lines are in general inexpensive and you can replace them yourself with parts from say AutoZone. You will need some vac caps/plugs/fittings from the HELP section and/or the section where they sell the emissions, oil and air filters. They come in blister pack assortments. As for vac hoses, you will find that a few feet of the three smallest sizes will work. One very easy way to get them is go to an AutoZOne or NAPA and ask the counter person to look under the hood of the car to see the sizes of the tubing and guess at how much of each size will be needed. A good counterperson will also be able to reckon which of the fitting assortments you need to buy. There is not that much tubing in the '98 since the tranny is electronic. It will not be much $$ and all you need for installation is a pair of scissors or a box knife and an hour or so. The '95 has more tubing. Other thing is - the '98 is supercharged. Supercharged cars don't have all that much vacuum due in part to the constant charge of intake air thru the supercharger - consequently even when everything is working right, vacuum signals are in some cases fairly faint. Consequently, I will not argue with your mechanic since he does this for a living and I do not -- but I will say that for my money I'd go ahead and fix those (#*$&@#( leaks just to make the "signal to noise ratio" improve.

That is, the vac system was not designed to leak and was not designe to tolerate leaks. If your hoses have little cracks, that may not actually be where the action is in terms of leaks. They will be leaking at the nipples attaching to the vac fittings, because the hoses won't hold tight. You can't see those leaks per se, although you could spot them with a smoke machine.

So... If you have an hour or so you ought to just go ahead and fix the vac hoses, then at minimum the tranny repairs (if any) will be that much more useful. And besides, fix it now and you'll get rid of those parasitic leaks at the vac fittings that you can't see anyway. So that although this may not *cause* the problem if you fix it now it won't *contribute* to the problem either. Done right, you wont have to mess with the vac lines again for a long while.

As for the wires - there was another series of posts where another Riv owner got some wires that were bad new. The Riviera comes *stock* with a very high powered ignition system. The stock coils are for all intents and purposes just as bang-y as the red or yellow ones that look faster. If your plug wires were not replaced with OE or better (Delco, Magnecor, what have you) it wouldn't surprise me to find them having problems after a year. Running common plug wires on an SC Riv with a good stock ignition system is like trying to run fire-hose pressures and volumes of water thru a common garden hose. Water will run but the hose will split before long no matter what you do. Again this might not be the *cause* of the problems but is probably *contributing.*

Thanks for your summary, and I hope things go well.

Albertj

Albert, I really appreciate your post. That took some of your time and you made me go out and buy some vacuum lines right after

The two lines that were cracked have been replaced. I drove the car right afterward and it didn't make a difference with regard to my problem, but indeed it gave me a little more peace of mind regardless.

The wires were replaced by the shop with lower-grade non-Delco wires about a year back, allegedly. I'll get some new AC Delco ones in there next weekend though, and we'll see what happens after that. My PCM recently threw out an odd code, so I'll probably be getting that reflashed next weekend as well. It'll be a fun 2 days

so now with sound vac lines and plugwires, time to deal with the tranny.

Albertj

ZEP wrote:

My PCM recently threw out an odd code, so I'll probably be getting that reflashed next weekend as well. It'll be a fun 2 days

What do you mean by an odd code. Do you know what the code is.?
And what do you mean by having the PCM re-flashed.? I'm curious.

Rick, I can't recall the exact code. I always work with the guy in the bay and he showed me the code. The first code I got maybe 1.5 months ago was that the fuel was running lean, and getting a new SC gasket helped fix that problem. But the SES light stayed on, so I took it in again to get it scanned (I can't wait to buy a scanner some time soon), and my mechanic showed me the code. Something like: CPM Sensor Out of Range."

So, they replaced the camshaft position sensor. The light stayed on though even though he cleared it, and the car gave us the same code... CPM Sensor Out of Range. So he doesn't know what to do. He'll check it again some time this week to see if everything looks alright, but he said that he thought the computer might need to be re-flashed.

That's just what he told me... I've heard I may need to have a CASE Learn procedure done, not a re-flash, but I'm not sure, so I was just going to hold out on that until I get the wires done next weekend.