Thread: 98 Grand Prix GTP 3800 II, Troubleshooting Rough Idle and Sluggish Acceleration :(

Yes, there is something else that is causing the sputtering. Could still be a vac leak. I don't see any reason to close the gap that much on a stock car. Sure it works, but there is still an underlaying cause that requires a small gap.

Give the EGR tube a look (the accordian looking tube) and spray around there for leaks as well. Often the tube will crack in between one of the accordian bends and not be visable, which would create a leak.

Ok i am getting the obd 2 reader today so i will spray all the fittings including that one amd post what the sensors are doing

Im running 91 i am going to remove that egr tubing and replace the gasket on the egr valve too, i should be getting my obd2 reader in a few hours so i will know the fuel pressure

Ok egr tubing is good, sprayed all vac fittings idle stayed the same. Hooked the odb2 and ran yhe scans not sure what im looking for tho. I will try to make a report and post the results next. The car seems to be running worse now than it was last. Im going to pull the plugs out and set tge gap back at .055 and see what that does. Any ideas

Originally Posted by BillBoost37

FM..you know I'd say remove the tube and look. Only because I and about 10 others have agreed..no amount of spraying can vet out a bad EGR tube. it's someone blocked from sucking in the spray.

I'd also suggest checking the fuel pressure. Your plug gapping shouldn't have to be that small.

What octane fuel are you running?

Good point. If it's truly hidden then spraying really wouldn't work there I guess. I'll file that into the banks for future use.

When you scanned the car did it say anything like catalist inneficency or downstream/upstream 02 sensor out of range?This really sounds like the problem ALL grand prix have especialy the gtp's.If your converter is original that may be your problem.cut that guy off and put yourself a magnaflow hi-flow on there.around here you can take those converters to a metal recycler and get 90$!! so its win win really.I see these cars in all the time here at the shop with melted down converters.probaly on account you have the wrong plugs in it.you dont need an upgrade.stick with original plugs(should be ac delco platnuim and you will have alot less troble out of it.unless you have a "suped up" ride(further more than gm's tiny supercharger) the gap it should be at is on the catalist sticker under you hood(where it says engine size and other various legal crap) i belive its .45 but you might want to look.one other thing you might look into is a coolant temp sensor.when those go bad the car will rev up and down untill it warms up.in combination with a bad cat,wrong plugs,gapping and a bad sensor i could see how it would stall after a few moments.doesnt sound fuel related as it stays running if you give it

Ok, just got a copy of UVscan and i will do a log and post the results tomarrow. Any requests as to what filters to set to log or how to drive the car while scanning.
Thanks

Ok the obd2 scanner i have will not link to uvscan, the iac has already been replaced, when i hit thr cat from the bottom it rattles, at some point someone down the road already did a down pipe and looks like the cat was replaced then too. But is there any test i can do to confirm bad cat?

Ok should i set the plugs back at 060 before i poll the o2 sensor or should i leave them gaped at 045
Just to check i pull the o2 sensor before or after the cat

Quivk update, while scanning the intake manifold was reading vacuum at 10 to 11 at idle around 800 rpm. Started to smoke the vacuum lines and realized it was leaking at the maf tps and iac. Removed the intake tube and all the sensors on the throttle body used ductape to seal everything off. Smoked the system again and smoke was coming out of the the throttle body where it meats the supercharger manifold. So i removed the throttle body and the gasket was trashed. Ductaped the supercharger manifold where the throttle body goes smoked the system again and no more leaks. Getting a new gasket and will put it all back together and see what the vac reading is. Think i finally figured out where the vac problem is. After i get it all put back togethet i will refap the plugs at 055 and take it for a test drive. Them i will yank the o2 sensor out and take it for another test drive. I will post the results when all is done.

Ok my vacuum reading is at 18 while in part at idle its at 790 rpm. Fixing to gap the plugs at 055 and go for a test drive.

If your cat is already rattling then its bad.theres no point in risking breaking the o2 sensor taking it out just to check a cat you know is bad.

I know i ran out of money, i get paid friday so i will cut it off and get it replaced. Is there a certain type i should go with, i called some local shops around my area in floruda and they quoted in the 200 range for a high flow cat. I am almost confident that the cat is causing all the problems. When i hit it it rattles. When the car is cold it runns great when its hot it has trouble in all ranges of the power band. Also i can grab the tail pipes after 20 mins of driving and they are not even warm. I cant wait to replace the cat i will post an update once its replaced. should be sometime friday. I quit driving the car because im not sure if a clogged cat can mess up otherthings, can it?

Ok I got a high flow cat put on the car, and the one they took of was the orignal one. The problem still exist only when the engine is warm. I just purchased new injectors, new coil packs, and upper and lower intake manifold gaskets. I should get them in a few days. I am going to just start replacing everything untill i figure this thing out. i am not sure what is left to replace....... Just a quick update on items that were replaced. MAF, IAC, TPS, Fuel pump,fuel filter, Fuel pressure relay, Plugs, Plug wires, Catalitic Converter, Throttle body gasket, All new silicone vacuum lines, EGR gasket, New belts, Fresh synthetic oil, Flushed tranny and replaced filter, Seafomed gas tank and Vac lines, New coupler on supercharger, 3 inch down pipe. And i think thats it. Update as to what it is doing. When the car is cold it runs great, no idle problems, Fast acceleration. When the engine gets to 180 it has trouble starting and will not hold the idle unless you feather it and slowly bring down the idle to normal rpms at 900. Once you get it started it will stay started and does not die when you let of the gas. When you accelerate it bogs down and is hard to get up to the speed limit. not sure what else to replace i am open to all ideas. PLEASE HELP

Oh i forgot i was running the plugs gaped at .035 to fix the spark blow out when boost would hit. i will set the gap back at .055 once i get home and see what that does for me. i am still at the stock pulley but i have a 3.4 sitting here but scared to put it on, want to get the car running good first. i get updates straight to my phone so i will respond as soon as some one else posts here.

Thanks

Once you get the gap set see what you get. Other than that, maybe check the fuel pressure w/ a gauge and see what its at. I know you put a new pump in but who knows.

And yea, wait on that 3.4. Unless you have the supporting mods for it you will be risking the motor for sure. If you haven't read it, take a look at the "Safely modding your 3800" post to see what you need to run this size. Hate to see someone go through all this just to chip a piston on a 3.4.