Rough idle and stall when cold

Tiny
WOLF10EV
  • MEMBER
  • 1991 NISSAN 300ZX
  • 3.0L
  • 6 CYL
  • 2WD
  • MANUAL
  • 56,605 MILES
My car starts fine but will not idle unless I keep my foot on the throttle until it warms up a good bit. It sounds great and no miss at all when revved up but does have somewhat of a miss when warm and idling. I have made various setting changes at the TPS and it does seem to have some effect. I have done this with two different TPS sensors. Do I have an injector problem even if it sounds great when revved and could it be something else?
Thursday, March 24th, 2022 AT 10:08 AM

5 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Normally a rough idle when cold is due to an air fuel imbalance. So that means we have a fuel pressure issue that gets better when the engine warms up.

So let's start with checking the fuel pressure just to be sure it is not the issue. Here is a guide that will show how to do this:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

If this checks out then we will need to check for a vacuum leak.

Basically if you have unmetered air coming in then the PCM doesn't know to adjust for it. However, once it is warmed up and it starts looking at o2 sensor data, it is able to compensate for it and the idle smooths out.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Once we run through these two issues we will have a better idea where to go.

Thanks
Was this
answer
helpful?
Yes
No
Thursday, March 24th, 2022 AT 4:47 PM
Tiny
WOLF10EV
  • MEMBER
  • 3 POSTS
Thank you so much.
Was this
answer
helpful?
Yes
No
Thursday, March 24th, 2022 AT 6:17 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
You are welcome. Please let us know how this turns out. We are curious to see what the solution is.

Thanks
Was this
answer
helpful?
Yes
No
Saturday, March 26th, 2022 AT 9:27 AM
Tiny
WOLF10EV
  • MEMBER
  • 3 POSTS
I'm leaning towards it being a faulty TPS. In shopping for new one's I wonder why there's a difference in them do NA cars vs Turbo cars. How much different could they possibly be?
Was this
answer
helpful?
Yes
No
Saturday, March 26th, 2022 AT 2:51 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
They operate the same but the voltage readings they give are slightly different for the module to respond to. You will want to stick to the correct one for your engine.

Let us know how it turns out as that info will surely help others.
Was this
answer
helpful?
Yes
No
Sunday, March 27th, 2022 AT 7:15 PM

Please login or register to post a reply.

Related Engine Idle Rough Content

Rough Engine Idle
GUIDE
Rough Engine Idle
A rough en­gine idle con­di­tion is a com­mon is­sue that many dri­vers face of­ten in­di­cat­ing un­der­ly­ing prob­lems within the en­gine, fuel or ig­ni­tion sys­tem. We have cre­ated this...
VIEW MORE