J30 Transmission or MAF or Throttle Position or ???

[BobWilson]

First I want to thank everyone here for many great tips. I've been able to fix so many things and learn a ton thanks to you guys.

Now I have one that's stumping me. Here's the story...

One day a couple of weeks ago when pulling out the car died. No big event, just didn't go and I saw it had died. Put it in N and started it, pulled off with a foot on the gas and brake and made it home. Died once more the next morning under low power after pulling out of my driveway, again it started, and no more trouble that day. I start reading about the MAF, so I bought a can of cleaner to start with and sprayed the crap out of it.

Everything seemed to be fine. Low idle was much better and no dying in low RPM settings.

Then a bigger issue started. At interstate speed, where it was great before, it occasionally will act like the transmission is disengaging. RPM stays steady - no revving - but a lurching that usually pops back, but once it starts doesn't go away until the car is slowed. This seems to happen worse when the car is fully warm. Drives to and from work (7 miles) don't get it to that point, but driving it again before it can cool seem to be worse.

Today it started again so I pulled off an exit. Idle at the light was fine. After pulling out I thought it could be a problem with OD, so I dropped it to 3rd thinking I could bypass the problem. I was rolling down hill and not under power. It lurched slightly after moving to 3rd and as I pulled to the light noticed it had died again. It started right up and I came home on slower backroads with no issues.

I did the AT diagnostic test and no codes came up. All 11 lights flash quickly. The car is a 1994 with almost 158,000 miles. I originally thought this to be a MAF issue, but now I'm thinking it could be the throttle position sensor (although no AT code) or something more sinister - the transmission itself. I checked the fluid a week or two ago and it looked pink on the dipstick.

Anyone have any ideas or experience with an issue like this? I appreciate any help I can get.

Thanks,
Bob

[yodawill2000]

Hello Bob.
As you probably know there's quiet a few things that can cause that.
Time start start eliminating.
It does seem to be a MAF issue but one cant be sure.
Have you cleaned the MAF connector and Applied Dielectric grease to the contacts before putting it back together ?
If a signal is intermittent from the MAF the ECU will go nutz.

[BobWilson]

Thanks for the reply Yoda,

I have cleaned it, but not greased it. I sprayed the cleaner through the mesh. Is that good or do I need to get closer to it?

[yodawill2000]

Thats all I ever do.
If you got a good shot on the element you should be golden.
The reason I think its the MAF or something else electronic is it happens after warm up.
Also you said the engine dies out.
Cant see how the transmission would cause that.
That's a GOOD thing as far as the cash flow goes.
Same theory goes for the TPS.
I'm a old gearhead so the theory I use is the engine needs 3 thing to run.
Fuel,Air and spark.
One of those are missing if the engine dies out.
Or its flooding.
When you start it back up have you noticed any black smoke coming from the exhaust ?

[BobWilson]

No black smoke. At least not enough to notice. It starts right up, never a problem there.

Agreed on the engine dying. That's why I went for the MAF or TPS first. I guess if either keeps getting worse that trans problem could be the next thing to start happening. I was kinda hoping to see the AT diagnostic tell me it was the TPS but it didn't.

As for the MAF is that wiring connector a pain to disconnect? I've tried it a couple times and it's not cooperating. I ended up spraying the MAF through the tube with a towel behind it cause I couldn't get it off the car.

Another funny question - I sprayed that in the direction of the air flow. Would it also be a good idea to spray it the other way? Or could that mess with the sensor?

[yodawill2000]

Good question.
I too do it that way about 4 times a year.
Seems to work fine.
The TPS definitely decides the shifting point for the transmission , but I don't see how it can kill the engine.
Has the check engine light ever came on when this happens ?

[BobWilson]

Yeah, this feels more like a disconnect than a shift. It's definitely not shifting down, as the RPM stays the same. So the engine stays at the same place based on where the throttle is, yet the car slows. So feels disconnected.

Could the loss of MAF signal be saying to stop flow of air/fuel since no signal means no airflow? Is that how that works?

The one thing that keeps me wondering is this hasn't happened at lower speeds. Would a lower speed, meaning less air flow, mean the MAF is not as critical? I can't see how it could be less important going slow than going fast but maybe?

Oh, and to answer your question - yes, once I noticed the light come on and then it jumped slightly within a few seconds.

[BobWilson]

I just had a thought... Have you ever heard of a fuel filter issue causing this? Would that explain why this happens at higher speeds? More fuel through the system meaning dead filter more likely to cause a problem?

[yodawill2000]

Other than a few cut up knuckles there's only one way to find out !!
Air Filter and Fuel filter need to be replaced a few times a year.
Now that Ethanol is being shoved down our throats one must be aware of the crud its pulling out of the tank to the engine.
I have replaced the fuel filter several times since Ive had my J.
And every dang time I'm amazed how nasty it is.
I always cut it open so I know what is going on.

[GerryO]

Read that you've run an AT diagnostic and pulled codes, but have you pulled engine codes?

Know that the engine won't run long with the MAF disconnected and my lone experience with a dirty MAF was with my '97 F150, which exhibited slight engine misses at the shift points and occasional violent bucking at freeway speeds under very light throttle pressure. The harder I drove the thing the better it ran.

Once tried to start the engine with the TPS disconnected and it would not start, but TPS output voltage adjustment does involve disconnecting and reconnecting the TPS with the engine running. TPS adjustment has a big effect on idle speed (engine speed with the throttle plates closed) and isn't there also a vehicle speed sensor that also plays a role? Some Z32 guys have had issues with non-stock intake set-ups.

Sounds like something engine temperature and idle speed related, Air Regulator/AAC/IAC/Idle Adjustment Screw or possibly even a vacuum leak that's causing the fuel mixture to lean out and stall the engine. I'm a big believer in plenum pulls for cars with this number of miles and age.

[yodawill2000]

I hope to pull mine before spring to address a aggravating Valve cover leak.

[GerryO]

I hope to pull mine before spring to address a aggravating Valve cover leak.

There are so many good things to do in there that can be done so much better with everything taken apart, in terms of just taking things apart, cleaning them up and putting them back together again, and all for the price of a few o-rings, gaskets and hoses. Makes changing spark plugs easy too. Far better and safer than a Sea Foam or similar treatment and things go back together again much easier and more quickly than they come apart.

Watch out for quite a few really nasty sharp edges on the plenum casting. I did a lot of filing on mine, while it was out of the car.

[J30tChumpCar]

Our cars will not run with a disconnected or failed MAF(yours could be in the middle of failing) it is a very important primary input that may not always set a code, cleaning should be done in the direction of airflow as thats where debris will collect on the front facing airflow elements, poking one screen "cube" with the cleaner straw to enlarge it enough to get a closer blow is sometimes necessary, also trying another unit to confirm if the issue is with the maf or not my be necessary. My local you pick junk yard usually gets $20 or so bux for one, even if it doesn't fix things it can be stocked for later or sold for profit on craigs list as the 300zx guys covet them as well.

The metal clip can be gently pried off with a pocket knife blade in the center of the long side, be careful to keep a finger on it as it will fly.

[BobWilson]

Update: not the fuel filter. And I threw in a new air filter for fun. Next up the MAF. The more I drive and have the same issue in different conditions, the more I move away from my initial thought it was a transmission possibility.

@J30tChumpCar - Good idea on the junk yard. I hit my local PullAPart a couple of Fridays ago with this in mind, but I think the MAFs get pulled off as the cars are coming on the lot - not a single one to be found. Coil packs everywhere, but no MAF.

[J30tChumpCar]

I found the same issue but lucked out on one J that was dismantled to see bent valves before being junked, MAF was in the trunk.

300zx guys harvest certain things off j cars as soon as they hit the ground, the trick is to beat them.

[BobWilson]

I'm not very familiar with the EGR valve, but could a clogged one be a cause? I'm assuming they get clogged up with carbon.

One extra thing I've noticed is on the occasions the car has stumbled lately, if I press the gas it seems to behave better. Even a quick stab of the throttle helps. It seems to me this could be more air over the MAF, the throttle position sensor, or if it's a clogged EGR maybe forcing more exhaust through. Anyone have thoughts on this?

I'm still hoping it's the MAF, but I'm hedging my bet in case it's not.

[GerryO]

I'm not very familiar with the EGR valve, but could a clogged one be a cause? I'm assuming they get clogged up with carbon

Don't think it's the EGR valve, as they don't really kick in unless manifold vacuums/engine rpms are high, adding some engine knock protection by dumbing down the air/fuel mixture and it's not unusual to delete them totally, plus a leaky EGR valve would be a bigger issue than clogged EGR tubes.

http://www.google.com/url?sa=t&source=w ... IyQqVvpyeQ

Brake vacuum booster related? What does the trouble-shooting section of the FSM have to say?

[BobWilson]

I'm not sure about the brake booster idea, but one of the airtight tests is to pump the pedal after a brief warm up. After a short trip this morning I did that and it got tighter each time - the sign of an airtight system.

[BobWilson]

Weekend Update - Got the new MAF and quick-changed it, since I'm getting so good at that. I'm happy to report that so far she's running much better. No lurching at speed and idle much smoother. So I think it was the sensor going out.

Hopefully that's the end to this thread. If not I'll be back. And I hope someone else will find this along the way and it will help them like all the previous threads have helped me.

Thanks again to everyone for ideas and help.

[J30tChumpCar]

Fingers crossed.. Where and how much was it?

[gsf1200s]

digging up an old post, but did the MAF solve your problem. I am having the exact same issue with my 93

[BobWilson]

Yes sir, for me that did solve the problem. I bought one off Ebay for $80 and it's still working fine. I've seen some posts saying those Ebay versions don't last long, but I figured at that price vs. new I could buy several before I hit the cost of new.

I don't put many miles on the car, but in calendar time it's lasted longer than some suggested it would.

Hope that helps,
Bob