I have 2001 3.8 engine...95,000

Iv been reading up on this and saw a few similar issues and I'm still trying to figure this out.


It will shift fine until it gets warm/10 miles of driving.. it will start to shift erratically and wine. its shifts erratically at about 3 mph and 18 mph then it will smooth out.

I will cut the car off, pop the hood unplug the maf sensor and the problem will go away...even if i plug the maf in right away after, it takes some time to come back.

Iv been through three maf sensors, cleaned the throttle, idle air etc, changed trans fluid and filter, checked fuel pressure and regulator...with no change.

I have a p0420 code but that's it.

I'm starting to think maybe the pcm is bad.

 

Disconnect battery , leave it for 10 min, and try it.. see If it still is screwed up.. Have you put it on a scanner?

 

Have you checked continuity on the maf plug to PCM?

 

I disconnected battery and just drove it to school..no time to see if that worked yet...

I have a P0420..and the maf low circuit code only when I unplug the maf of course..thats all, no freeze frame data.

When you say continuity would i check the leads in the maf plug?

 

Yes your goin to see if you have a solid path between the PCM and the maf plug.. Where do you live?

 

P0420 is a catalyst efficiency code.. I can't see that screwing tranny stuff up unless its plugged , but since your fine minus maf, I'd look elsewhere..

 

Near Chicago...so I just put multimeter probe into maf plug and one in the other ..example one probe in the far right and one in the middle..and then check middle with far right left...

Just making sure and should battery be disconnected?

 

When i was having issues, "not trans issues" i had to do cats and maf to fix it...factory cats??

Id think its probably transmission related though..

 

yes factory cat..if cat was plugged it would probably perform this way, whether maf connected or disconnected.. even when cold...maybe I'm wrong...

I guess I may need to drive it with maf unplugged for a while, to see if it comes back even when unplugged.

 

Could be caused by a bad MAF, those engines we crazy for MAF problems. Tap on it with a screwdriver with the engine running and see if it acts up. Replace it if it does. I also would check into the 420 code. Does the converter rattle? If the catalyst is moving around, and intermintly causing problems too. Most of the time its a bad MAF, and old converter that is no longer working within the tight epa specs. Hope this helps!!

 

have you bought a used factory maf? its gotta be the maf if when you unplug it its fine /

 

Use an Oscilloscope to properly identify if your MAF is the issue. You can google the test and there are a few places that will give you a "walkthrough" on it. The connector can also be the problem... you may find that the break/corrosion in the wire is not right at the connector either, but as far back the leads as 12"s!! Moisture can "creep" up the leads and corrode the wire that far back. Just something to look for..

 

The converter doesn't rattle...

When I first bought the car it had a bad maf and had a maf code, I would tap on it and the engine would stumble.. I immediately replaced it

- I replaced it with a aftermarket unit (bwd)..it would idle funny at start up and have same problem as now.
-I got a new car-done brand maf..same as exact problem as now
- Now I have a used oem maf..as my gas mileage is steadily getting better the stumbling problem is still the same.


So I'm really going to have to look into the Oscilloscope test and testing the maf wiring..


Its just crazy before it gets warm it runs good ..great pickup and everything.

Ill let you guys know what I come up with, Thanks.

 

The reason your car runs good for the first 10 minutes or so is because the computer has a set tune to feed the engine. Once the car is warmed up to operating temperatures only then does it use the MAF and other sensors to gather information to determine A/F ratio.

 

UPDATE...Drove it today until it got warm...started to do the same thing..disconnected maf..and ran exactly the same...Wow....That's crazy but Maybe I know where my problem is..I'll still do the maf test though.


I'm almost sure its trans related..maybe trans pump.. at this point because it starts to whine.. simultaneously.

Thanks for all your help thus far...

 

When you unplug the MAF the transmission goes to max line pressure because the pcm can not determine the load on the motor with no maf signal. Sounds like your trans is on its way out.

 

That's what I'm thinking also, I may add some seafoam trans tune.. and see if that helps, maybe drop the pan again.. whether it helps or not I guess I may as well drive it until it completely goes bad. I headed to trans shop in the morning...


Thanks

 

Bingo!

 

Turned out to be the trans ..p1811..just wanted to give the update.

I'll try a shift kit and see if that helps.

Thanks everyone.