1995 GMC Jimmy Bad idle

Tiny
SIXONEFOUR
  • MEMBER
  • 1995 GMC JIMMY
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 163,000 MILES
I have a 95 GMC Jimmy 4.3 Vortec (CPI) 4x4 with 163k miles.

Problem:

The RPMs rev between 500 and 1500. It almost feels like its choking and sometimes stalls at the bottom. It fires right back up every time. The idle spikes up and down and continues this nasty cycle. It gets better as the truck warms up.

Recently changed:

Idle Air Control Valve
Fuel Filter
Tune up (Plugs/Wires/Cap/PCV/Rotor Button)

Several people have told me it needs a new Spider Injector. Is there anything else I can rule out or check before I invest the $300 for the injector?

Any info and advice is much appreciated! Thanks!
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Wednesday, November 10th, 2010 AT 11:02 AM

8 Replies

Tiny
RASMATAZ
  • MEMBER
Check the fuel pressure if its within specs if okay. Test the throttle position sensor and manifold absolute pressure sensor-also look for vacuum leaks
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Wednesday, November 10th, 2010 AT 1:31 PM
Tiny
SIXONEFOUR
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I also suspect a vaccum leak or a fuel pump problem. Is there a way to test the spider injector? I had the intake open today to find very small puddles of fuel. It was also filthy. Keep in mind it is 16 years old. Thanks for the info!
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Saturday, November 13th, 2010 AT 4:16 AM
Tiny
SIXONEFOUR
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I had the truck hooked up to a diagnostic machine only to tell me the MAP sensor was reading low. I replaced the MAP sensor. It helped a bit, but did not solve the problem. How can I test the fuel pressure? Can I spray the vacuum tubes and around the intake with WD40 to check for a vacuum leak? I appreciate your help.
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Sunday, November 21st, 2010 AT 12:43 AM
Tiny
RASMATAZ
  • MEMBER
(I had the intake open today to find very small puddles of fuel.)
If the puddle is on the pax side-the FPR is leaking-if it's @ the driver's side it's the nut kit.
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Monday, November 22nd, 2010 AT 10:21 AM
Tiny
SIXONEFOUR
  • MEMBER
The fuel pressure regulator is a reasonable cause for my problem. I've since replaced the MAP sensor and the TP sensor. They made minor improvement. She still idles horribly. FPR is a fairly cheap part (Under $60).

I really need to have a fuel pressure and vacuum tests done. I will probably end up taking it to a shop for those.

Any other suggestions are appreciated! Thanks again.
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Sunday, January 2nd, 2011 AT 6:17 AM
Tiny
RASMATAZ
  • MEMBER
Inspect and clean the EGR valve and see what happens
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Sunday, January 2nd, 2011 AT 10:31 PM
Tiny
SIXONEFOUR
  • MEMBER
I swapped the EGR valve already, but it came from a junkyard. I also replaced the gasket. Thanks for your help! Any more ideas? I'm about to put some more cash into her this month. I have a FPR on the way and debating on just buying the injector. If that doesn't fix it, it has to be the fuel pump or a vacuum leak. Almost every sensor is new. The only ones I haven't changed out are the oxygen sensors, and the ambient air temp sensor (which is vacuum related as I understand at this point). I'll definitely keep you posted. Thanks again!
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Tuesday, January 4th, 2011 AT 1:47 AM
Tiny
SIXONEFOUR
  • MEMBER
Put a new injector in, cleared up a lot of the high idling, better fuel economy and more power restored. It is still spiking DOWN now and sometimes stalling around 500RPM. Still have a slight misfire.
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Thursday, January 20th, 2011 AT 7:07 PM

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