Has been backfiring thru intake. Had a dtc 0102, so decided it might be intake gaskets. Replaced all gaskets and checked all components for vacuum leaks. New plugs, wires are good, all sensors look good on scanner (maf, map, timing, tps). Still coughing. Anybody know what it could be.

Thanks, Jeff

 

P0102 is the maf code. Check the maf circuit, cleaning the maf and connectors couldn't hurt any either.

 

Thanks. The MAF is working great, as I can read it on the scanner. However, I suppose it could be an intermittent issue. Maybe I will run the scanner on MAF data display to see if there are blips while driving. The coughing is not frequent enough to see with the car in the driveway, and it never coughs while idling.

Thanks, Jeff

 

Perfectly working MAF sensor circuits don't throw codes. It could be the wiring heck it could be the PCM itself but 9 time out of 10 its the sensor. If its not the MAF sensor then the next most likely thing is the pig tail connector going too the sensor. Tap the sensor and wiggle the wires. See if either has an effect.

Intake gasket for a MAF sensor low voltage? That is a new one to me. Intake gaskets do go bad and leak vacuum, that is a common issue, but they cause high idle and I can not remember one ever setting a MAF code. Never hurt to do a 3800 intake gaskets they are more known for leaking coolant and they are the number one cause of engine failure in 3800.

 

The MAF code was not low voltage, as this sensor signal is frequency. Low frequency can result from reduced inlet flow due to vacuum leaks. Vacuum leaks do not cause increased idle unless they exceed normal flow thru the idle control port, but the idle did come down a tad after the new gaskets. The MAF code never came back after I cleared it over two weeks ago, but I agree it may be bad. Just hard to diagnose when it's intermittent. I will run the scanner tomorrow while driving to see what the signal looks like during a cough. I'm thinking another possibility is an injector going bad. I've been using injector cleaner for the last two tanks of gas. I will let you guys know what happens.

Thanks guys, Jeff

 

I have been working on cars with MAF sensor for 30 years, I have never seen a MAF sensor code caused by a vacuum leak. No one on this site has every fixed a MAF code by repairing a vacuum leak. I would guess 80% of the cars build before 2000 have small micro vacuum leaks that are compensated for by the IAC motor. I have seen cars that had Vacuum leaks so bad they would not go below 3000 RPM, no MAF code.

So you are say the Check engine light is not on and it is still stumbling. Last car I had with this issue that was very intermittent it turned out to be the pig tail going to the senors. I got lucky, I bumped the wires and the engine stumbled. After it settled down I could wiggle the wire all I want and it was fine and I know I wiggled the wire before that. I took the chance and replaced the connector, that was 3 years ago.... no issue since. before the car would stumble once or twice a day but not set the check light maybe 2-3 weeks.

 

Thanks Gorn. That is exactly what the car is doing. I think it may have been coughing a long time and never set a code. I only noticed coughing a couple months ago, then the code one time. But I remember it was running a little rough last year, so I went to clean the throttle and found a little hole blown into the flow straightener. I replaced the straightener and it still looks brand new. I will check the pigtail today. Maybe the sensor is not getting full battery voltage. Will let you know and thanks again.

Jeff

 

Update, I checked the voltage at the sensor--it is getting battery voltage across the B-C leads, no change as I giggle the wires. I will try giggling again when I have it running, but I wanted to ask if anyone knows the specs on the sensor. I am seeing over 28MOhms across A-C pins. About 10MOhms between pins B-C and infinite between A-B (after some capacitor charges). Does that sound right? Maybe there is an open resistor in the sensor internal circuits???

Thanks, Jeff

 

Another update. I drove the car about 20 miles yesterday while watching the MAF output on a scanner. The data looked perfect, even when the engine coughed (several times). Then, I stopped the car but let it idle while I giggled the MAF wiring and connector. Also rapped on the top of the sensor, but not even the slightest blip in the output. It may still be bad, but is working pretty good from what I can see. I think this is one of those problems that has to get worse before it can be diagnosed. :-(

Thanks for the help so far and any future ideas.

Jeff

 

I had a similar problem on another car.
My advice, if you try clean the MAF and the trottle body with the same specific cleaner.
It can only do good to both.