Help Engine Studder/Sputter


Apr 29, 2012
Hi guys, it seems I'm always chasing some kind of problem with this car, but you guys always seem to help me out so here goes. Sorry if its long i've included any information I think will help diagnose the problem.

I recently installed 42 lb injectors with matched TT chip, Walbro fuel pump with hot wire kit, and the rjc power plate for the stock plenum. After those upgrades, I was still having problems with knock, but that was fixed once I found out the hose going to the waste gate solenoid was completely deteriorated. After that was fixed the car ran beautifully.

NOW, two weeks ago when I had the car out to stretch its legs since it sits while I'm away at school, it ran beautifully and built boost without any problems until I got home. When I was pulling it into the driveway I noticed a really rough idle all of a sudden. I went to take the car out again later to see if was just having a temperamental episode but when I got it on the road, it would just sputter and hesitate under normal throttle.

This seemed to resemble how the car would run when up pipe would blow off due to my shitty clamps. Noticing that none of them had blown off I thought that maybe one of the rubber hoses connecting turbo, intercooler, and plenum had cracked due to old age, and the boost under cold weather. They needed to be replaced so ordered news and got myself some T-bolt clamps.

Before I put the clamps and hoses on today I took it for a drive. It drove normally for a minute and built boost once, then I had to limp it home with it sputtering. After I got all of the hoses and clamps on, I started it and let it warm up to 160, revved it in park and it seemed fine. Took it for a drive, built boost once and then had to limp it back again. So obviously they didn't solve the problem and so I began trouble shooting.

Here's what I've tried so far:
cleaning the maf (the maf caused a similar problem on my old GN)
changed the waste gate solenoid (every time the car sputtered you could hear the turbo shudder so I thought maybe the waste gate wasn't closing all the way)
I also tried taking the line going to the solenoid off to see if it would run normally without anything regulating the boost. Still nothing.

It seems that when I start the car, I can rev it in park without any problems, but then when I drive it, it will build boost once and then start acting up, then when I get it home and rev it, it will continue to sputter.

Here are the scan master numbers once warmed up
O2 600
AF 05
L8 36
Bat 13.6
Int 128
BL 118
Clt 168
Ats 57
r 800
Tps .44 (idling) .42 (key on) 4.50 (WOT)
Iac 27
Mal 00

Im sure this has no effect, but my battery has been going dead from sitting in the cold. So I have to jump it and then it is fine.
I live in PA and it was about 43 degrees today.

Im all out of ideas of what could be wrong and of course I just read the hot rod magazine that says the rjc power plate is no good and the gaskets blow. Is this true? Maybe a vacuum leak is causing it? I don't have a boost gauge since my car is almost completely stock, but I plan on installing one within the next week.

Any help would be greatly appreciated,
Take the battery and have it tested and charged if it's good. I wouldn't depend on the alternator to charge a dead battery after jump starting it,it may run but no way is it going to be fully charged and putting a load on it is not going to be good. And these cars don't run well with low voltage.

I won't even hook up my car to another one to give a jump start,because as soon as you hook up to that car what ever problem they have is now your problem. I do have a battery pack/jumper that i will you for that purpose if i have it with me.I will give them a ride to an auto parts store if needed.

Don't leave the battery in the car sitting out in the cold and letting it go dead,bring the battery into the house/basement and sit it on something like a piece of plywood,cardboard but not directly on a concrete floor. And if you have a charger hook it up and make sure it is fully charged for the next time you go driving. But if it's not holding a charge it may be time for a new battery. Not saying this is your problem but it is not helping things.
I haven't checked this yet, but if the Scanmaster doesn't show a drop in volts when the car is shuddering, is it safe to say this isn't causing the problem?
Just went out and drove the car. The volt reading stayed around 13.6 and didn't really drop when the car stuttered. What is going on?
Did you have to jump start the car to get it started before you took it out for the drive?

I hate to keep harping about the battery being the problem but that is what i think the problem is. And maybe a problem with the alternator also if you have been trying to charge the battery with it.

Next time you go out for a drive stop at your local auto parts store and ask them to do a charging system test on your car. They don't charge a fee for this service.
bring the battery into the house/basement and sit it on something like a piece of plywood,cardboard but not directly on a concrete floor.

I usually don't comment on things like this but I can't help it lol. This is an urban legend. Sitting batteries on a concrete floor does not discharge it. Many cars contain metal battery trays, parts stores store batteries on metal racks, all conductive materials. And yes, I have measured a battery that sat on the concrete floor for like a year and it still measured like 12.4v lol
How old is the battery in the car?
How old is the MAF on the car?
Do you have another battery you can throw in the car?
Do you have another MAF you can throw on the car?
When driving have you noticed if the TPS reading on the scanmaster ever fluxes at a steady throttle position?

The battery would be one of the things i'd change and see if it was the problem. Something doesn't seem to be right with the battery if you have it draining that badly sitting in just 40 deg weather that you have to jump it.
How healthy is the alternator in the car?
When driving what does the BLM and INT change to on the scanmaster?
Is the BLM still reading at 118 when driving or does it move around?
When driving what do the O2's look like on the scanmaster? Before it acts up, with a WOT blast are the O2's at least 750 or higher?
How old is the O2 sensor, it could possibly be marginal?
Have you thought about checking for leaks around the power plate and possibly removing the power plate to see if maybe that's causing your problems?
If it didn't act like this before the upgrades, i'd first make sure you had a good strong battery as it sounds like it has a cell that is starting to get weak.
Then if it clears up you found the problem, if not at least you have a stable power source ( these cars demand stable power to run properly ) and can move onto trying other things next. If it's all relatively stock like you were saying minus the bigger injectors, the walbro fuel pump with hotwire kit, also the adding of the powerplate, i would as much of a pain as it is gonna be yank the powerplate out and go without the power plate.
It seems like it's a touch too rich and the computer is pulling alittle fuel out to compensate for that based on the BLM being alittle lower than the ideal 128. Seems like there's a leak causing that to happen based on others that had similar problems with the BLM being lower than ideal.
The power plate won't really help that much in a mostly stock engine vs say a really built up engine that's making 10's and faster type power in the quarter mile.

I'd make sure there was a good battery in there and the charging system was good to go to include making sure that all grounds etc were all good. It sounds like that battery may need to be replaced. I'd make sure there was no leaks & verify the fuel pressure is stable and set correctly. Then i'd try to if another knowledgeable member was nearby get another set of eyes on it to help figure out what is the cause of the issue.

I'd get over to a credible autoparts store and get them to do a check on the charging system. Then go from there, but i'd avoid beating on it until you get the issue(s) resolved.

Sorry for the length of reply, just a list of some things to look at. Hope you get it figured out.

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Thanks for your help guys, but it was the MAF. I ordered a new one, but threw an extra one on for now.
A flaky MAF would do it, glad you got it figured out and had an extra MAF to try to see if it was that causing you grief.

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Yeah I was talking to my local specialist and he told me to unplug it and see if the idle cleared up which it did. He said that when the MAFs go bad they don't always set off the check engine light or throw any codes.
Glad you were able to pinpoint the maf as the problem and able to locate a source to order a new one.

Where did you order the new maf sensor from?

I hated when i had a maf sensor on my car. And when i was able to take it off and run my engine without it over 7 years ago (thanks to the MaftPro from Bob Bailey) i was just thrilled to death.And i wouldn't let a maf within 10 ft of my car ever

Oh and i still think you should have the charging system checked for peace of mind of just knowing it's good to go and there won't be any surprises when you are out driving.
I just ordered a remanufactured unit through auto zone. Thats what the local specialist told me to do since a newer LT1 maf and translator would not be necessary for my stock setup. It was $60.

As for the battery, I am not too worried about it. I can only assume it was just the battery that is bad since it has been fine ever since that first jump. The car was sitting for about two months without being started. Pair that with the colder weather and an old battery, Im not surprised it went dead.

I am going to figure it out but at least the car is back to running normally again.
The one I put on from my other car has a reman sticker on the bottom and it seems to be working fine. I just wanted a spare. I heard the AC delco ones are crap right out of the box I got a duralast one so hopefully it works. If not it came with a lifetime warranty.
Had this same problem and I was like 30 minutes from home. I limped hat thing all he way to my garage and didn't touch it the rest of the day I was so upset. It ended up being the MAF as well.

Glad u got it fixed!