P0101 + P0300 = ?

[tlynch]

Hi all:

I have a 2001 Chevy Tahoe with about 125K miles that doesn't get driven much. It has shown me a couple of codes over the past two months.

It started with a P0101 (Mass Air Flow Circuit Range/Performance), so I replaced the MAF sensor (even I can do this without bloodshed!). It felt like success for a while, but then it started throwing a P0300 (Random/multiple cylinder(s)-misfire detected). When the P0300 was cropping up, the truck would sometimes idle roughly, and stumble, or even stall, when accelerating from a stop or low speed.

Right now? No codes active or pending. Runs about like you would expect a 20 year-old truck to run, and I am puzzled.

So I am turning to the collective wisdom of the forum for ideas on what it may be, and how to rule possibilities in or out. I'm thinking that it may be a vacuum or intake leak as the common denominator of the two codes, but I know less than pretty much everyone here.

I am also open to suggestions on scan tools that I could use to watch misfire data.

Thanks for any help!

Edit to add: Changed the air filter when I was doing the MAF. I did get a pending P0101 for a bit after the MAF change, but it went away.

 

[PNWYukon]

A simple thing you can do is unplug all your connectors and spray them with Deoxit or other type of contact cleaner. Could be oxidation on contacts or not, but a good thing to do anyway.

 

[OR VietVet]

How old are the plugs and wires?

I would get some throttle body cleaner at the parts store and do a cleaning. Follow directions.

https://www.autozone.com/fuel-and-e...rzvjeiCv2kT5VxZIDPRoCuVcQAvD_BwE&gclsrc=aw.ds

 

[tlynch]

A simple thing you can do is unplug all your connectors and spray them with Deoxit or other type of contact cleaner. Could be oxidation on contacts or not, but a good thing to do anyway.

Thanks for the suggestion.

 

[tlynch]

How old are the plugs and wires?

I would get some throttle body cleaner at the parts store and do a cleaning. Follow directions.

https://www.autozone.com/fuel-and-e...rzvjeiCv2kT5VxZIDPRoCuVcQAvD_BwE&gclsrc=aw.ds

I don't know how old the plugs and wires are. I have had the Tahoe for about 1.5 years. And have only put 10k miles on it. The previous owner took good care of it. I'll have to look and see if he documented that service.

Thanks for the throttle body cleaning suggestion.

 

[drakon543]

what brand maf did you replace the assumed faulty maf with. an aftermarket maf might be showing the ecm its within range so it won't set a code but its not actually reading what it should be. when it decides to act up is it more so warm or cold? do you have access to a more advanced scanner you can use for an hr? i cant remember if you iat is in the maf but it can also cause similar issues. cold engine key on with an advanced scanner should show you what the ecm sees for ambient iat temps which should be very close to actual ambient. also check to see what it says your engine temp is cold and warm. same deal with then iat readings. if the ecm thinks the engine is cold/warm or thr same with the iat when its significantly different than what its actually at can cause some issues. lastly based off the question about when it acts up could be related to a failing intake manifold gasket.

 

[tlynch]

what brand maf did you replace the assumed faulty maf with. an aftermarket maf might be showing the ecm its within range so it won't set a code but its not actually reading what it should be. when it decides to act up is it more so warm or cold? do you have access to a more advanced scanner you can use for an hr? i cant remember if you iat is in the maf but it can also cause similar issues. cold engine key on with an advanced scanner should show you what the ecm sees for ambient iat temps which should be very close to actual ambient. also check to see what it says your engine temp is cold and warm. same deal with then iat readings. if the ecm thinks the engine is cold/warm or thr same with the iat when its significantly different than what its actually at can cause some issues. lastly based off the question about when it acts up could be related to a failing intake manifold gasket.

Thanks for taking time to respond.

Currently, my scanner is Torque Pro on my phone. I'll check what temperature sensors it reads. Last night I figured out how to add cylinder misfire PIDs, so I hope to collect more data on that. I am open to buying a more detailed scanner, but I don't use one often enough to want to go too far up the scanner food chain. I am open to recommendations.

I replaced the MAF with a Delphi.

I have had heavy engine missing both warm and cold. I have experienced heavy stumbling within 200 yards of my driveway when starting from a stop sign. I have also had the same heavy miss after driving 15 miles or so when beginning to accelerate from low speed when light turned green. The common element seems to be accelerating from no/low speed. My last two or three trips have had no problems at all.

The only change before those last few trouble-free trips was replacing the battery. I have not had either code, or heavy engine misfires, since that swap. I have thought of the battery as unrelated, but sometimes systems insist on relating things I don't expect.

I appreciate all the helpful suggestions I'm getting.

 

[tlynch]

Updates:

IAT reads at actual ambient temp.

I was able access misfire history. All cylinders had values at start up. Over 10-15 minutes running on my driveway, I saw increases in cylinders 3 (+16), 4 (+52) and 7 (+2).

Plugs and wires were replaced 5.5 years /23k miles ago. Throttle body was cleaned at the same time.

I have not yet started cleaning contacts or TB.

 

[drakon543]

torque pro works just fine for what you need aside from more specific things it might not see. you could have an intake manifold leak or just a vacuum leak somewhere on that side of the engine. back to the battery comment tho as thaf can potentially cause problems all over the truck. a battery thats not taking or holding a charge as well as it should is going to draw excessively from your alternator. left alone it would eventually take out the alternator aswell. during initial startup the battery handles everything but once its running the alternator takes over. if your alternator is struggling with the battery it can have adverse effects all over the truck with everything being under powered. so at the moment if the truck acts up again if its bad enough to notice at an idle or with someone touching the pedal. have a can of carb cleaner or starting fluid ready. you will want to run a heavy blast down the sides of the lower and upper sealing surface. lower where it bolts to the heads and upper where it bolts to the lower intake manifold. if the idle smooths out or suddenly changes for a moment you found a leak.

 

[tlynch]

torque pro works just fine for what you need aside from more specific things it might not see. you could have an intake manifold leak or just a vacuum leak somewhere on that side of the engine. back to the battery comment tho as thaf can potentially cause problems all over the truck. a battery thats not taking or holding a charge as well as it should is going to draw excessively from your alternator. left alone it would eventually take out the alternator aswell. during initial startup the battery handles everything but once its running the alternator takes over. if your alternator is struggling with the battery it can have adverse effects all over the truck with everything being under powered. so at the moment if the truck acts up again if its bad enough to notice at an idle or with someone touching the pedal. have a can of carb cleaner or starting fluid ready. you will want to run a heavy blast down the sides of the lower and upper sealing surface. lower where it bolts to the heads and upper where it bolts to the lower intake manifold. if the idle smooths out or suddenly changes for a moment you found a leak.

Thanks for the info. I appreciate your help!

I reckon I need to grab a can of carb cleaner when I buy a can of contact cleaner.