2000 Grand Prix GTP Surging Idle


cposada
05-20-2007, 05:02 AM
My 2000 Grand Prix GTP is surging (fluctuating, fluctuate, searching, search, surge) for idle. First off, a 3800 Supercharged engine. The car drove fine since new. Decided to run to the store for some dinner items and the car had an issue starting. It would turn over but die immediately. This was shortly after running the car so the engine was already warm. Anyway, the next morning the car would start fine and idle for about 3-4 minutes with no issues. Once the car is warmed up it starts to search for a proper idle: it will idle up and then down. Up and then down. This is all over a 1000+ RPM range. The car will eventually stall out and not want to be started again until the engine is cold. I changed the PCV Valve, Fuel Filter, Spark Plugs and Wires, TPS(Throttle Position Sensor), IAC(Idle Air Control), Oxygen Sensor(front and back), and checked the fuel pump resistor with the tab pulled back. I even changed changed out the resistor anyway.
Since this has occurred I have taken opinions from a number of people but have been searching the Internet, for a month now, as to what could really be the problem. My latest effort will be checking the Fuel Pressure Regulator as this has caused some people an issue. My initial thoughts(meaning when it first occurred) were that there may be a vacuum leak but the lines are good. Should I be checking somewhere else? I have also been told to spray Carb Cleaner/Throttle Body Cleaner in certain areas. I'm not sure where but maybe with a more detailed description of the location, and if I need another person. I could check this too. I was told this could be due to a MAP sensor or MAF sensor but I am leaning towards the Fuel Pressure Regulator. Is it possible, however unlikely, to be a combination of problems?
My questions are whether I can disconnect the MAP or MAF sensor to check to see if the idle evens out? What tool(s) do I need to check the fuel pressure at the Schrader Valve? Where would I spray the cleaner to check for possible vacuum leaks? If it is a leak, could it be the head or valve cover gaskets? How do I check the fuel pump, in the trunk of the car, and its connections(I read that the contacts could be corroded or not making a good connection)? How do I clean the Throttle Body(what do I take apart) and what is the PLENUM(whether it be upper or lower)? I will reply and notify everyone of my results as I go. I will detail my actions as most people will not understand (namely me: my first time dealing with a computer controlled engine) EXACTLY what I am doing and I want this to be helpful to many others. Any other thoughts on why this is occurring would be greatly appreciated. Sorry for being long winded but I want to solve this myself. If you only know the answer to one of my questions I will happily accept it and continue to let you know the result. I'm eagerly awaiting your reply and thanks to all who respond.

BNaylor
05-20-2007, 10:47 AM
Welcome to AF and the Grand Prix forum.

You do not have a UIM plenum that the normally aspirated SII 3800s have problems with. The supercharger is the upper intake manifold. To check for vacuum leaks at the throttle body and intake manifold area the best thing to do is connect an automotive vacuum tester (0-30 in hg). Acceptable engine vacuum will read in a range of 15-22 in hg. Or you can spray carb or throttle body cleaner around the area where the supercharger mates to the lower intake manifold and look for changes to idle/rpms. Also, around the fuel injectors at the cylinder heads and at the throttle body flange.

To start since it is the easiest thing to do disconnect the MAF sensor. The idle may be erratic until the engine warms up but should stabilize.

If that doesn't work or make any difference then check fuel pressure with an automotive fuel pressure tester. Auto parts stores sell them for $30-$40. Actron is good brand and has a bleeder valve. I would do this before messing with the fuel pump area. Look for a range of 48-55 psi.

The fuel pressure test will check for a flaky fuel pressure regulator (FPR). You will run a test with vacuum connected and disconnected and look for a deviation in excess of 5-6 psi.

cposada
05-20-2007, 04:12 PM
Thanks bnaylor! I will check the MAF once I get home. If the idle issue goes away with the MAF disconnected can I safely say that I just need to replace it? Can I drive the car with it disconnected? If yes on my last question, why do I need it? With the MAF connected can I expect better performance, fuel economy, or a smoother running engine?
I will try and get a fuel pressure tester as well.
Thanks again for the quick reply.

BNaylor
05-20-2007, 09:10 PM
In most cases yes. You can drive the car for an indefinite period of time or until you get the replacement part. There may be some loss of fuel economy but no loss of performance that I know of. As I mentioned earlier there may be some idle bounce until the engine warms up but it should stabilize. The computer uses the MAF sensor for better control of the fuel injection system especially in open loop mode.

cposada
05-21-2007, 11:09 AM
When I got home I tried disconnecting the MAF as you mentioned. The cars idle is normal again. I called my local parts dealer and they have one for $219 minus a $70 core charge which brings it back down to $139. Apparently the old one can be fixed/rebuilt if they want the core. Thanks again bnaylor, I really should have come to this forum much sooner than I had. The response was quick and I spent a month just reading the forums before I posted my own issue. Thanks to Automotive Forums also.

BNaylor
05-21-2007, 11:15 AM
You're welcome and glad you found the forum helpful. Be careful with reman. MAF sensors like A1 Cardone. High failure rate. The best deal for '99 and up Grand Prix L36/L67 is at ZZP. That is for a new GM MAF and no core charge to worry about. Good luck.

http://www.zzperformance.com/grand_prix/products1.php?id=378&catid=107

cposada
05-21-2007, 01:24 PM
Hey bnaylor, you're the man. I checked out ZZP and am going to order from them. What do you think of cleaning the MAF as mentioned in this thread http://www.automotiveforums.com/vbulletin/showthread.php?p=3170928#post3170928
I have the Electronics Cleaner already. I won't try till tomorrow as my girlfriend works today and needs to get there. Do you only moderate the Grand Prix forums? Your knowledge has come in very helpful.

BNaylor
05-21-2007, 01:44 PM
The cleaning of the MAF wire element is mainly applicable to K&N drop in or CAI/FWI oiled filter equipped cars. The filter oil may contaminate the MAF. However, cleaning is a good idea first and doesn't take much time. You will clean the wire element in the plastic tube once MAF is removed from the throttle body (TB). 2 Torx T20 safety screws hold it onto the TB. Use the electrical cleaner only on that part. Also, clean the TB inlet screen. With throttle body or carb spray cleaner clean the TB inside bore and IAC seat/IAC if you have not done that already.

I can moderate any forum on AF but my permanently assigned is Grand Prix, all Buick and all of Oldsmobile. The GP forum is my home since I started out as regular member here. You'll find alot of the regular members, Advisors and Moderators on AF very helpful. Good luck and let us know how it turns out.

Add your comment to this topic!