QuestionQUESTION: Dear Experts,
I own a 99 Grand Prix 3.1 liter v6 with 110,000 miles on it and I have a basic knowledge about cars(at least mine). Recently, the car was running hot. I replaced the thermostat. Took hours to get to it and only seconds to replace, go figure. Anyway, Problem fixed. However, when I tested the car to check the temp gauge, the C.E. light came on. I realized the "computer chip" to the MAF sensor was unplugged. I plugged it in and the car idled rough, rpms changed constantly and the car would eventually stall (CE light turned off when i put the sensor on). I've researched this problem and determined that those are textbook symptoms for a broken or dirty MAF sensor. A quick stop at Advance auto parts and I bought a new air filter and MAF sensor cleaner. I took the air intake apart, replaced the air filter and attempted to clean the MAF sensor. I took off the clamps and unscrewed the "metal bracket" that houses the sensor. I was able to clean the tiny wires (wasnt sure if there were supposed to be 4 of them or if the 3 I had were the right amount, if Im missing one I suppose that would trigger the CE light) I looked on dozens of forums and every pictured instruction (of different makes and models) shows the owner taking the MAF sensor out entirely and cleaning it. I couldn't do that because it seemed that the plastic surrounded most of it. I cleaned what I could and reassembled the car. Problem remained. Not only did the CE light stay on after I plugged the "chip" in, the car still idled rough and stalled. However, when the sensor was out, the car ran fine and didnt jump at all. I could actually say that its runs as if the sensor was in place. Since I would like to sell the car in the near future, what can I do? Will Napa , Autozone or Advance Autoparts run a free diagnosis for me? If not, who will? Are there any problems with leaving the car the way it is and ignoring the light?(besides not knowing if another problem exists because the light will always be on)Any way to get the light off without fixing the problem? Not sure if this is enough info for anyone to help me but thanks in advance and I will followup with the problem codes that the computer spits out whenever I get them.
p.s. Obviously, my last resort is buying a new MAF (150 bucks or used on eBay for 60). Any suggestions, if there is any, are greatly appreciated.
-Anthony
ANSWER: Hi Anthony,
First I must say I wish I had 100 customers like you as far as your detailed story of what was done.
Did you remove the upper intake to replace thermostat?
Just a question.
First If you take it to a parts store or most repair shops, they'll offer free scanning of computer controlled systems, but most won't give you free diagnosis.
Meineke Car Care, Pepboys are a few I know that offer free computer scanning, Most will though just scan it for you and tell you the code.
As you stated, Autozone does also.
If you could get that for me, I'll have a better idea of what to search.
In the mean time, make sure (if you did remove intake) the TPS (throttle Position Sensor) connector is securely attached. Make sure the MAP (manifold Absolute Pressure) sensor is also securely attached and the vacuum hose to it is also securly attached.
If possible to avoid you spending $$$ on the sensor it may not need, It MAY be worth it to have it diagnosed, so the repair shop can check these items data, along with the MAF sensor. The data in this circumstance will probablly pinpoint the fault (given a good diagnostician looks at it)
I understand you need to get this resolved quickly, but if you WANT to get the code # from a free scan and give it to me I can get diagnostic sheets and help you out there.
Unplugging the sensor will make it run good short term, but it will create other problems, fuel economy issues, etc..
Let me know I'll be here to help.
Good Luck
Paul
---------- FOLLOW-UP ----------
QUESTION: WOW.. its incredible that you responded this fast. I have professors that don't respond to questions about my final exams in days and you respond in hours. FOR FREE! If I could meet you, I'd shake your hand, haha. In regard to your questions: Due to the fact that I'm a novice in the automotive world, I can only assume as to what the upper intake is. I'm almost positive that it had to be taken off, not because I know what it looks like, but because the thermostat is located so deep in the front end that quite alot of things needed to be taken off. My guess is that its located there just because its a midsize car and not a big F-150 with alot of space. Anyway, the air intake was taken off along with several air and water pipes that intertwined (all were put back and clamped) I had to disconnect and reconnect a fuel line which was angled so ridiculously that I would love to confront the man who designed it and give him a piece of my mind.(I broke that line and had to buy it from the dealer, probably shouldve mentioned that, sorry) Due to some improper tools and not having my own mechanic shop, several things that probably didn't had to be done, were done. But I guess thats what you get for "doin' it yourself". If you can check a picture of the engine (3.1 Liter v6) I can tell you that the big cover that has 3100 written on it that covers the entire engine components and is held in place by 16 or 18mm bolts (Bare with me, it was above 10mm thats all I remember haha). Thats my guess as to what the intake is.Is it called the intake manifold? Just taking a stab at it. Also, I worked with a friend of mine (who knows alot more than I about cars) and I will get a better description as to what exactly was done and report it back to you. I will also bring the car for the scan. Im guessing that scan gives you the codes as to what the problem is and the diagnosis is a detail of what that code means? Another trick to make money I guess. Also, about how much does a diagnosis cost?
P.S. I hate to admit it but I left a valid piece out of the last description. It will be hard to describe via the internet and without pictures but I will do my best. There is a plastic pipe that is secured on the top/middle area of black rubber "tubing" that makes up the air intake. This plastic pipe is located within 3 inches north of the MAF sensor. This plastic tube connects to the back of the engine "area", as in behind everything and out of plain view. This was cracked while replacing the thermostat and was "repaired" with electrical tape. I can't for the life of me find where it connects too. I know what vicinity its in but the bugs started to attack me in Florida and I put it off until tomorrow. :) .I ran the car and didnt feel any leaks from the pipe or any air coming out. I figured it was a "bs" emmisions regulation or something to keep the air cleaner. It remained unplugged before and after the car was turned on (another possible reason for the CE light??)Next, I do not have an owners manual for this car so I will have to get back to you about the MAP and TPS sensors. Know of a good website explaining them with pictures? I won't be selling this car for a few months so I can "afford" to do it myself and learn in the process. Although, a good man knows when hes in too deep, so I will take off my mechanics hat and take it to a repair shop if Im in over my head. Last question, you said that unplugging the MAF sensor now will create further problems such as fuel economy, etc. To be honest Paul, if thats the worst of the problems then Im fine with that. What exactly can leaving it unplugged cause in the future? I guess give me a scale of 1-10 on importance. Thanks for any and all help you have given me thus far and taking the time out to respond to my questions. It is much appreciated Paul.
-Anthony
AnswerAnthony
That black "pipe" goes from the PCV valve (on the front valve cover) and crosses over "plugs" into the Upper intake (the large aluminum plenum that has "3100" embossed on it) and then goes and attaches to the EVAP purge solonoid.
Your vehicle may be sucking air from this hose that is cracked. Just a little bit, will throw off the amount of air entering the engine. It is MORE than what the MAF sensor is is reading. A vacuum leak.
Believe it or not, I had a MAF problem this afternoon and I found the yellow wire broken inside the insulation about 1" from the MAF sensor connector.
have the vehicle running and "wiggle" the harness see if it clears up, or if it changes the way it runs.
If so, you may just have a wire problem.
Scale of 1-10 I would say about a 5. Fuel economy and poor running at times. Poor occasional acceleration. We'll get it fixed.
MAP sensor is the square sensor mounted on the rear side of the Upper Intake (3100 cover lol) The TPS has a round plug and is mounter on the throttle below the MAF.
Your correct also a scan they'll just give you the fault code number and possible causes. A true diagnosis will follow a set chart and pinpoint (USUALLY) the exact cause of the fault (be it wiring, sensor fault, etc...)I charge in most cases an hour for the diagnosis unless the chart gets very detailed, I'll then charge by the hour. Hourly rate in your area I'm not sure, but here there is no shop $15.00 lower than any other shop. They all stay pretty close and competitive.
I really hope I help in some way, we'll get it.
Again, good luck.
Paul
