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

I was having a somewhat similar problem, but it appears that it's been fixed. I want to give it a few days before claiming 100%, but after replacing the ignition coils (with a used set off ebay, with ignition module, for $36), my car has so far been acting better. I was having problems when the engine was under load - not all the time, but much of the time. It seemed like the engine didn't like to rev, or if it did rev fine, it would hit a point and then just drop off out of nowhere.

I took the car out for a few test drives today, and it didn't give me that trouble once. Also, the car seems a little quicker to start up, which makes me think there was at least one weak coil in there somewhere. We'll see what happens over the next few days, but I would suggest looking at the coils. (BTW, I had replaced the spark plug wires and plugs already).

Well, after a week, I can say that the "new" coils definitely fixed the problem! I've got better throttle response, especially at highway speed, and much better performance when the engine is under load. So if plugs and wires don't help, I'd definitely suggest coils next.

Thanks for the update, Brad!

Brad95Riv wrote:

Well, after a week, I can say that the "new" coils definitely fixed the problem! I've got better throttle response, especially at highway speed, and much better performance when the engine is under load. So if plugs and wires don't help, I'd definitely suggest coils next.

I agree! This is what I said earlier.

We seem to have a split as some don't seem to believe coils are the problem

I wasn't doubting it was the coils, but would always suggest plugs/wires first for a spark-related issue.

Lies!

j/k. Me too, just coils next if you have the money.

NO 4 EVR wrote:

Lies!

j/k. Me too, just coils next if you have the money.

That's why I bought them on ebay. A bit of a risk buying used, but a heck of a lot cheaper in case the coils aren't the problem.

But, as mentioned several times, it's better to try the plugs and wires first. At the very least, you'll have a tip-top shape ignition system when all is said and done!

Good thinking buying used in case. I wouldn't of thought of that.

Lets see where do I start......

I have a 95 riv S/C, completely stock. When I first start the car in the morning after sitting all night, the car rus rather well, like most do. After running about 10-15 minutes the check engine light comes on. At that point I notice that the rpm's tend to drop and the car has a bit of a studder. Now when I say drop, I mean they fall to around 5-600, now thats with the car in drive. When I shift to neutral the rpms go back up to around 11-1,200 and the engine smoothes out. Once back in drive it does the same thing. Now when the car is in drive and I'm actually moving it drives rather nice. however I do feel a bit of hesitation on 1/4-1/2 throttle. When its WOT there is no hesitation whate-so-ever. It goes, no questions asked. Now a little background information as to what I have tried with no luck. First I checked and replaced intake filter. Then plugs. Even checked for a vacum leak. first 2 things didnt help and I couldnt find a leak. Now I was reading just about everything I could find on this site about series one engines. I came across a couple of people that had similar issues and it was a result of coils. Now this car possibly was sitting a while before I bought it but im not sure, but common sense would say to check fuel filter however I havent had much chance yet to crawl under the car to search for it. Anyone know where its hiding? Any other ideas as to what I could try to get this car to run smoother. I love my riv and dont want to give up on it, however......

Next part of my post would have to be about pulling some performance out if this car. Obviously I wouldnt do anything performance wise until I get this annoyence resolved, but as far as simble bolt on items to boost the car a bit, I'm looking for some ideas. I know there isnt much out there for series 1's, but what i had in mind was some suggestions for:

Exhaust
pulley's
ignition
cam(i know its not bolt on but i love taking things apart and putting back together)
suspension
and a scan tool...I looked on ebay, and a few parts stores and came up with nothing......some help?

ANY AND EVERY SUGGESTION WOULD BE MUCH APPRECIATED AND WILL BE CONSIDERED.

First of all, welcome to the forum! Don't get frustrated with the riv, I'm sure it's a minor issue. We just have to find it. You said you changed your plugs...you ought to go ahead and change the plug wires. Usually the coil packs don't go bad. But if it will make you feel better, you can pull them and Auto Zone can test them off the car. The fuel filter is located under the car kinda right behind the door. It's easy to spot. You might think about doing a top end clean using Seafoam. Seafoaming gave me a LOT of throttle response. You need to find out what kind of code you are throwing. Unfortunately, Auto Zone can't read our codes. The curse of the Series I. To address your future mods;The rest of the curse is that you can't do much with a scan tool. You can change the Down pipe on the exhaust but you won't get much more HP from playing with the exhaust. I'd suggest the smaller S/C pulley, cam and suspension products. The cheapest upgrade for suspension is the strut tower brace. Well worth the $40.
and then you can do the sway bars. How many miles are on her?

Welcome. Maybe a good idea to clean the MAF sensor. Carefully remove it; use electronics spray cleaner to remove the dirt. Good luck!

welcome. It really helps to know 1) where you're from and 2) the mileage of the car. If you're from Canada, you can go to canadian tire and "rent " an obd-1 scanner to see what codes are showing up. Just take advantage of their no-questions-asked return policy. I'm sure some stores in the US function the same way.

Anyway, bad mafs are known to cause the symptoms you describe. Check you maf. Also if you have a high mileage car, give your throttle body (TB) a good cleaning and make sure your idle air control (IAC) is clean too. If anyone has the manual can you give him the proper series 1 IAC adjustment procedure?

First let me thank everyone that has answered so far. To answer some questions, I live in Wisconsin, United States. The car has 146,000 miles. The motor was "supposedly rebuilt" at 105,000. I'm going shopping at the parts store tomorrow, here is my shopping list so far, anybody please tell me what I'm forgetting:

Plug wires......and recomendations?
T-Stat 180
Seafoam.......I have never used before, what exactly am i looking for?

Factory plug wires are very good. About $65 from the dealership.

factory wires wire the best for the money. anything cheaper and you may regret it down the road. the seafoam comes in a white can with red lettering. there is a write-up on how to use it in the FAQ section. you can also pick up a can of STP throttle body & intake cleaner. this is safe to use to clean up the TB and MAF sensor.
good luck and welcome to the forum!

Ok, here we are again. Once again thank you for the responses. I worked on the car all night tonight and here are the results. I replaced plug wires, cleaned the MAF and sprayed down the inside of the throttle body. The car does a run a BIT smoother, accelerates quicker, however I can still feel a bit of a studder while cruising at 1/4 throttle. And also when i am stopped at a light, the car idles at 700 which isnt too bad, but I still feel that shudder from the engine. A not smooth feeling. The good thing is the RPMs dont bounce around anymore. The SES light is still coming on though. Out of curiosity, when do the fans kick in, and if there not coming on when there supposed to, could that throw the light? Lets see, what else........oh yes, I changed the T-stat to a 180. I like the cooling results. Only problem is I cant get the water neck to seal now. I hate using silicone but it looks like I will be. I bought a new gasket, which I thought looked wierd. But when I pulled the water neck apart i was like "ok, thats how that works." Now is that gasket like a O ring and goes right around the T stat? I noticed a groove in the new gasket kind of like the T stat should fit right in. Someone let me know what I'm doing wrong. Next, what else can I do to fix my throttle issue? I feel like I am RIGHT THERE. I think the wires and spraying the MAF made a big difference as far as response. Now because this is my first Series 1, does anyone have any recomendations as far as what order Mods should be done in. I dont know how responsive and sensitive this engine is. From some of the FAQ it seems like it can be VERY.

Sounds like you're getting closer. You really need to find out what code you're throwing. It could be the EGR valve or God knows what else. I still think you ought to do the top engine clean with seafoam. It may not fix it BUT it will make a noticeable difference. As far as the t stat...I've changed mine but I can't remember what the gasket looked like. I think there is only one way for it to fit and yes, I did use silicone. Glad you went with the 180 stat. Before you spend any more money, get that code checked out!

yup, get the code read and address that issue. If unrelated I would verify IAC adjustment and clean the IAC passages (ask someone with a 95 where it is on the series 1). clean/check EGR, verify front O2 sensor (it may be all covered with carbon after all that mileage).

note on the T-stat there are 2 gaskets. A rubber O-ring and a paper gasket.

If you can't find seafoam, go to a GM parts counter and ask for GM top engine clean (liquid, not spray). Follow the same procedures using that. Don't forget to ask for your 20% discount (they always say yes). Definately do this, but check your plugs after as they may foul.

Jason wrote:

Don't forget to ask for your 20% discount (they always say yes). Definately do this, but check your plugs after as they may foul.

Not always.

WTF! I never get 20% discount! How does that work?

When i did the t stat, while taking it apart, there was only one gasket. The rubber o ring.

perhaps the series 1 doesn't use one? if it's the same t-stat, you could always get the paper one. I had to ask for one from a regal gs when I did mine.

When I go to a gm parts counter, I always just ask for the garage discount. I just tell them I'm a mechanic and need their part for a customer. If you want even better prices, check out discount gm parts somewhere on this site. Contact Dal Slabaugh and you can get your parts at cost + 10% + shipping (not inflated)

I have never cleaned an EGR or O2 sensor before. I wasnt aware you could actually clean them. At least not the EGR. Procedure??? Also to ask a previous question again, where do I hook a boost gauge up to?

go get your codes read. If it turns out your EGR is fubared, then just R&R.

[edit]EGR shown in pic below[edit], but try the other easier stuff first.

EGR is shown between the valve cover and upper radiator hose.