91 240SX auto hesitation saga continues - Update

[alexh]

Well,I posted before regarding a fairly severe hesistation problem. The car is an auto and sometimes (only when it's well warmed up) there is a very noticeable hesistation when I step on the gas from a dead stop. It only happens when the car has been idling for at least 10-20 secs, like at a stop light. A few times it has been so severe that I basically had no throttle for a few seconds and I though it would stall. Car has no trouble codes.

Car runs excellent otherwise at all loads/rpms.

So, since I first started looking at this problem, I have gone through all of the diagnostic procedures listed in the manual and a few others recommended by members here.

Since then the problem has worsened somewhat and I noticed some other symptoms as follows-

Once when driving, I had severe hesitation on acceleration from a stop. What was different this time is that I noticed lots of black smoke coming from the exhaust and the engine continued to run really rough. However, at a stop the engine idled normally! It's just when I step on the gas that it runs like crap. As I drove I jkept noticing lots of black smoke coming from the exhaust. After about 10 mins of driving the problem cleared up and it began driving normally.

Does this shed any additional light on the subject?

Recent tests I performed are:

Tested MAF sensor according to manual. . All voltages were within normal range (about 1V warmed up and idling).

I hate to throw out a guess here, but is it possible that an injector is stuck open? Of course it would mean it never really gets stuck at idle which would be really strange.

Somehow, off idle, the engine is getting way too much gas. The only thing I can think of is TPS or MAF is telling the computer that the load is much higher than it actually is, which causes a rich condition.

I have tested both TPS and MAF but we have to remember that the problem is intermittent.


Modified by alexh at 12:29 PM 7/6/2007

[ddgsxr504]

I know nothing about 240 auto trannies, but it sounds like you may have a vaccuum leak somewhere, associated with the transmission.

[thomasjamal]

Any luck with this?