I have a 1999 pontiac grand prix gt 3.8 3800 series 2 v6 recently i blew one of my spark plugs and wires to cylinder 6 i fixed that and the misfire that came with that problem

Michael Singer

Asked by Feb 08, 2015 at 06:22 PM about the 1999 Pontiac Grand Prix 4 Dr GT Sedan

Question type: Maintenance & Repair

My engine still chugs at idle and wants to
shut off its fine at start up until the car
warms up then it starts to cut off or after i
shift into gear and shift into neutral or park
it chugs and cuts off i was thinking egr
valve or throttle position sensor but i do not
really want to pay for a dyno diagnostics for
a stupid sensor neither do i want to go
down the list and replace ever single sensor
or thing it could possibly be and waste time
and money anyone have any ideas?

9 Answers


did you try the code reader yet but it does sound like the problem could be the EGR valve


Well, here's the cheap fix. Buy a can of throttle body cleaner and thoroughly clean your throttle body and IAC valve. Here is a video on how to remove your throttle body. The IAC valve should be the black piece on the right side of the throttle body with the plug. Take that off and clean all carbon out of it. https://www.youtube.com/watch?v=Pv- aSwGj6g4 If no improvement, you will be forced to start replacing parts. If the Pontiac is set up anything like my Camry, I'm guessing there are 3 spark plugs on the backside of the engine that are impossible to get to. If they are, do you know if they've ever been changed? That may be throwing a misfire code still. If I were to guess, I would say replace the EGR. Then I would replace your radiator temp sensor, then ambient air sensor. Something is telling your computer that the engine is ice cold when in fact it is not. I'm guessing that it's running too rich and killing the engine. That's why it runs great until it warms up.

Michael Singer

Yes i just changed the plug and wire to 6 i have the rest of wires and plugs havent changed it yet waiting for it to warm up a little ther is no more misfire just the chug i replaced the coolnt a few months back and when i changed wire 6 and plug for 6 i also changed the ignition coil pack for 3 and 6 im just thinkings its a dumb sensor like map sensor or throttle position sensor or egr valve or something like that im gonna finaih changing the plug and wires and replace my fuel filter and lines and run a 2 part fuel system cleaner all this week i was just trying to figure out which sensor it was it runs fine for the most part except poor fuel economy and its letting off a lot of carbon the shutting down just feels like it wants to go but is confused maybe just wrong fuel to air ratio or something not measuing enough volts something stupid


Since you're seeing black smoke (carbon) out the tailpipe you have an overly rich (too much fuel) air/fuel mixture. Could be the fuel pressure regulator. Check the vacuum line going to it. Could be split or disconnected. HTH. - Jim


Could be, could be, could be a lot of things. Why are you so averse to doing diagnostics? Change your plugs and wires. If one was bad others might be too. Take Reelin's advice about cleaning the throttle body(but ignore everything else he said about randomly replacing part and hoping for the best), since you can do that for about ten bucks and its a good maintenance practice Then hook a code reader up to it, even if you have to pay someone a few dollars to do it and find out what's wrong with the car and replace just that part.

Michael Singer

Yeah im gonna finish the plugs and wires this week idk i just always thought the diagnostics was expensive as hell and i ddnt want to pay 100 dollars just to be told which sensor it is or w.e ill try cleaning the throttle body i have the obd 2 code i misplaced the paper so idk what code it is exactly right now but it was all the fuel injector and like o2 sensor or throttle position sensor little computer problems lol atleast hoping i think it was p0107 but im not 100 percent but the main reason for that code is the map sensor and that sensors 50 to 75 bucks which isc i just dnt wanna spend 75 on one sensor and have that not be the problem and have to spend another 75 on another sensor or part


Yes it could be a lot of different things. Without the car in front of me it's hard to diagnose based on just the poster's description. The fact that black smoke is present is a sure sign it's dumping fuel. Throwing new plugs at it will make it run well for a day or two until the new plugs get gasoline fouled again. Then they'll be back to square 1. Some people on this forum don't have the money to waste on parts that don't fix the problem. Good luck with this. -Jim

Sharon West

Call around some shops will do a free diagnostics test my 1999 poniac Grand Prix Sent was doing the same thing I changed the Map sensor and the Mass airflow MAF sensor and my car is now running great and I didn't have any diagnostics done on mine I just read the book and my gut feeling said, that was the right thing to do and my gut feeling was right so try that after you, finish the plugs and wires

Sharon West

My 1999 poniac Grand Prix SE is also a 3.8 V6 3800 Series 2

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