1995 GMC Yukon Idle Surge When Warm

[Mule]

1995 GMC Yukon (non-Vortec, OBD1, TBI), ongoing for about a year, after truck was taken out of storage for 13 months:

 

Always smells a little rich.

 

Cold start – Long cranking, smooth idle. Smells very rich.

 

Warm start - no codes, no SES light, warm start (30 minutes off after full hot), short cranking, initial smooth idle; surging idle starts after 20 seconds. Feels like stalling, then catches itself and goes up to 800 RPM, then drops and repeats. Smooth idle and ride after about 1 minute. Smells rich/flooded. Not as bad in the summer, but very bad in cool weather.

 

Overall, it seems like something heats up, cools off, but not all the way cold, then either malfunctions or gives a bad reading to the computer which creates the surging. After a minute, it either warms up enough to stop malfunctioning or giving the computer bad info.

 

I have been to nine shops and they can all duplicate the symptoms, but can not track the source.

 

Thank you for any help!

 

No change after any of these fixes:

 

03 Jan 2012

Replace Coolant Temp Sensor

Replace coolant temp sensor connector

 

11 Jan 2012

PCV replace

 

12 Jan 2012

Replace Fuel pressure regulator

Replace driver’s side (left) fuel injector; it was dripping

 

14 Jan 2012

Clean air filter

 

24 Jan 2012

Replace Dist cap and rotor

Replace ignition coil

Replace Ignition Control Module

Tighten Idler Air Control Motor

 

31 Jan 2012

Replace IAC and pigtail

Replace O2 sensor

 

08 Feb 2012

Replace fuel pump

Replace fuel pump sending unit module

 

05 March 12

Replace fuel filter

 

08 March 12

Replace Spark Plugs (AC Delco Rapid Fire #1)

Replace Spark plug wires and heat shields

 

10 April 2012

Removed Jet chip to aid diagnostics

Replace Throttle Position Sensor

Replace PCV hose

Replace elbow on rear of TBI crankcase breather hose

 

25 April 2012

Replace MAP Sensor AC Delco

 

01 June 2012

Replace vacuum hose from A/C accumulator to heater control valve.

 

02 July 2012

Replaced TBI plastic ring and rear breather vent hose

Sea Foam spray into TBI

 

30 Nov 2012

Re-install Jet chip

Replace EGR valve

[black128412]

stored for 13 mos look close for a mouse in the house, had at least 5 newer chevys with crazy issues only to find chewed wires to ecm/pcm. then check with motor warm hold just over idle and spray non flameable brake clean around intake to valve cover area and base of TBI. TBI to intake gasket check/replace and if any flutter off idle w spray pull intake. if i remember and this is 5.0 5.7 they had aluminum intakes. they will warp and distort gasket. if you pull intake inspect around ports for cracks or crushed gasket. DO NOT USE AIR TOOLS TO CLEAN OLD GASKET OR HEADS!. air tools will destroy trueness of both surfaces. clean with good carb cleaner and hand scrap hard stuff with razor blade and hand sand 80 plus of higher depending on how bad they are. while off use straight edge (roofers square) lay across ports, shape should be true or damm close. also 5.7 i have seen a few break a head bolt so pull valve covers and toqure to spec to see if one is weak. other than that there should be a port in front of TBI unit maks sure no carbon, and also check vac to brake boster, boster could be bleeding off vac and make motor surge, hope it helps

[Mule]

From the top:

 

1. No signs of any rodent/bug/animal contact. Storage was a very clean facility with animal control.

2. Did the spray for vacuum leaks a few times over the last few months with no change in idle. TBI gasket was replaced last week.

3. Not at the point yet to start pulling the intake off, yet.

4. Checked the brake booster vacuum line and it is good. New brake booster 4 months ago for a different reason, but no change in this problem.

 

I do feel that it is a vacuum leak I am chasing, though.