J30 Hesitates/Stumbles After Sitting At a Dead Stop

[RocketCityJ30]

Hi,

I came across this forum today looking for some advice on a recent problem with my J30. What a great wealth of information!

However, I didn't find a good answer on my current problem. After sitting at a stop sign or traffic light for about a minute, the car stumbles/hesitates (sometimes almost dies) before taking off agian. It will do it almost every time, and it is worse with the air conditioner on than when off. Otherwise, the car runs fine.

Took it to my mechanic, who decided it had a cracked driver's side exhaust manifold. That set me back $500, and it didn't solve the problem (car is a little quieter now though). Now he says the passenger side manifold needs to be replaced, for another $500.

Any advice on this would be helpful.....

And Wes, if you have a link to the 1994 J30T FSM, I would appreciate you sending it to me at [email protected].

Thanks!

John

[Defiant]

Although you don't want to run with cracked headers, they're too late in the system to affect idle that way. Search the forums for idle issues having to do with EGR clogging, and dirty throttle bodies. Also, make sure your check engine codes have been read.

[RocketCityJ30]

Thanks for the tips. I thought the cracked manifold was a stretch. Now I have seen diagnostics say to look for a corroded ground on the O2 sensor on the manifold, or a bad O2 sensor.

He read the check engine codes, which he said led him to replace the cracked manifold.

I used to have several Tauruses that had this problem occasionally, and the solution was always to have a shop run intake cleaner through the system, but this mechanic hasn't suggested that on the J30.

[Defiant]

He read the check engine codes, which he said led him to replace the cracked manifold.

Ehhh... you may want to do some looking-into another mechanic. ECU codes are generated when a sensor returns an out-of-value reading. I can't think how you'd ever get one saying anything about a manifold. You commonly get a code when an O2 sensor fails, but there isn't one for the casting. Sounds like profit-talk.

Or, you could have some kind of supranatural mechanic, and it's prophet talk.

[RocketCityJ30]

I know what you are saying. The story continues to change on the reason he replaced the manifold, but as you did point out, it should have been replaced, just for different reasons. I saw the old one....it was cracked inside.

Today he replaced the plugs, even though I just replaced them last year, but that didn't help. He reprogrammed the ECU with his computer, and that didn't help. He then cleaned the intake system, and that also didn't do it.

He says the ECU indicates no sensor failures or fuel injector failures, but I assume the ECU can't determine sensor faults within the normal sensor reporting range, even though the sensor calibration may be off, such as a MAP sensor going bad. The ECU does indicate a misfire at the time the stumbling occurs.

This is really getting frustrating..........

I thought all mechanics had supernatural powers, or that's what they tell us!

[Defiant]

Today he replaced the plugs, even though I just replaced them last year, but that didn't help.

Well, might as well throw those at it. Nobody'll say they're a bad idea.Quote » He reprogrammed the ECU with his computer, and that didn't help.[/quote]I'm a little iffy on what that procedure was, or what it was supposed to have accomplished. Modern ECUs like this are constantly self-tuning, compensating for wear and conditions.Quote » He then cleaned the intake system, and that also didn't do it.[/quote]Have the EGR tubes been cleaned out?Quote »

He says the ECU indicates no sensor failures or fuel injector failures, but I assume the ECU can't determine sensor faults within the normal sensor reporting range, even though the sensor calibration may be off, such as a MAP sensor going bad.[/quote]A sensor "going bad" is by default out-of-range, and by definition "bad" to the ECU. Of course, if he's "reprogrammed" your ECU, that would have erased your failure codes.Quote » The ECU does indicate a misfire at the time the stumbling occurs.[/quote]A misfire on what cylinder? You're at a place where it might wind up cheaper to have an actual Infiniti dealership go over the car.Quote »I thought all mechanics had supernatural powers, or that's what they tell us![/quote]I think those are utilized when figuring up the bill.

[Skapunk4everr]

Ehhh... you may want to do some looking-into another mechanic. ECU codes are generated when a sensor returns an out-of-value reading. I can't think how you'd ever get one saying anything about a manifold. You commonly get a code when an O2 sensor fails, but there isn't one for the casting. Sounds like profit-talk.

Or, you could have some kind of supranatural mechanic, and it's prophet talk.

^ ^ The unfortunate thing about numerous mechanics is that most of them know what they are doing but to rack up a strong bill, they will lead you to other problems to "fix" or else your car will expolde.

Now i actually had a simmilar problem with my 1995 j30, and i replaced my MAF and that fixed my problem. I do not know if this will be the case for you, but it may be worth a shot because MAF's are roughly about $50 i think( dont quote me on this) but thats about what i paid for mine,minus labor, i put it in myself.

Good luck!

[RocketCityJ30]

Thanks again for the replies and advice. Today, I think he finally found root cause, although since he did a number of things, he is not sure which one actually fixed the problem. Among other things, he thoroughly cleaned the entire intake system again, and cleaned the MAF. Don't know if he cleaned the EGR tubes. Like skapunk4everr's problem, my money would be on the MAF sensor, but who knows. We settled up that he left the new plugs (he used Iridiums) in and the total new bill was $150. I hope that ends this chapter in our J30's life.......

[Defiant]

If you got through that for $150, you made a killing.

[yodawill2000]

cleaning my MAF took about 3 bux ..

[Defiant]

cleaning my MAF took about 3 bujx ..

Ah, but braver than many you certainly are. Wisened are they who know not to tempt the force in lands they have not before ventured.

[yodawill2000]

lolActually I plan on cleaning it once a year.Takes all of 5 minutes.