Chevy & GMC Vans

some of you may know of my engine studder/miss from the other board. Well i've been trying to track down a recent growing problem along with this miss/idle drop when stopped at red lights.

The problem now is a lot of stumbling/missing that happens at part throttle when accelerating, (The studder goes away and the engine perks up instantly when you push the gas down further). It has a really rough idle along with a miss and now idle surges at lights.

After researching and testing i tried replacing the MAP sensor...no change.
Changed the IAC valve...no change. (3 recomendations)
Cleaned/checked EGR valve...no change.

Checked for vacuum leaks, none found so far. (Will check inches of vacuum saturday)

Recently changed within past 2-3 years:
Plug, wires, cap and rotor
Throttle position sensor
Fuel pump
Fuel filter

I tested the coil today and it seemed to check ok but got a golden yellow spark when checking the coil directly when cranking. I'm going replace the coil with a friends known good coil to rule that out.

Any other ideas? This is driving me nuts!

Hi safariobsession
Hmmm, Just a shot here, but maybe check the Cap (for arching), Faulty fuel regulator, or to much advance in your timing (fualty knock or crank sensor). The best thing to do first is narrow it down to fuel or spark, then work into it from their safariobsession, not much I know, but I hope something helps here.

hmm.. i don't really to have anything to add to this one.. but, my 94 has always ran a little rough (and noisey) since i bought it 3yrs ago. i've never resolved it. i'd like to. so i'm going to follow this topic.

it passes etests no problem, doesn't smoke, gets normal gas milage. things i haven't tried are crank or knock sensors.. or the ign module. wouldn't mind knowing where the crank and knock sensors are located on a W motor.

sorry if this seems like a jack.. but, it does sound like the same problem.

rob

Thanks for the suggestions. I thought i'd add that on my 220 mile ride home from college, i ran winALDL for about 2.5 - 3 hours and had a pretty high number of "spark counts" at highway cruising speed (2200 RPM). The counts were up to a few thousand counts mainly between 1600-2400 RPM. Scary??? Bad??? Like I said though, the van regains power and loses its horrible stumble at higher RPMS. Is is a for sure weak coil????

Hi safariobsession
Check the Cap and Rotor first. Look for signs of arching under the cap itself. I would go through the electrical first safariobsession, that would be the easiest to do. Start with Cap,Rotor then work into it from their. I'm thinking a Bad Cap, Plug Wire, Plug (Crack Insulator) with that spark count. It could very well be shorting coil or Faulty Ignition Module, but that's where I would start personally speaking. Hope this helps, please keep us updated, Thanks.

well.. my update on this one is this.

changed the cap, rotor plugs, wires, coil AND ignition module this morning... oh.. and cleaned out the egr mine still runs the same with what seems like a slight miss or odd idle. at rpms it seems smooth. good thing i work at a parts store eh?

good luck with yours safariobsession hope you get it resolved... looks like i have to live with mine the way it is

Seems like you've thrown alot of money at ignition parts, granted you'll need em' sooner or later so a wise investmet. My 90 tbi does the same thing--runs fine--espesially cold [before closed loop] and then as ya hit a red light and stop the engine does the "I'm acting like I'm running outa gas thing" and stutters but doesnt stall--then tries to run at an idle only popin' it in neutral cures. Removed the air filter which was toasted-no change. Cleaned throttle body with spray-no change. No vacuum leaks that I can detect..[always used the propane method] With dash lights that dim excessively with turning on the headlights and all the goofy electrical gremlins with these vehicles wiring harness, I'd not be surprised that it's an ecm thing. At hard braking at a traffic light the oil pressure takes its customary dive as rpm drops off-then motor stumbles as if trying to recover--could the oil pressure cutoff switch be reching its threshold and be sending eratic signal to the ecm??? Ever take a 350 v8 and dial the idle down to where ya could visually see the fan blades individually as they spin...My bets on the oil safety circuit........just a thought--what do you think V8Familyman? Any method to my madness?

Seems like you've thrown alot of money at ignition parts, granted you'll need em' sooner or later so a wise investmet. My 90 tbi does the same thing--runs fine--espesially cold [before closed loop] and then as ya hit a red light and stop the engine does the "I'm acting like I'm running outa gas thing" and stutters but doesnt stall--then tries to run at an idle only popin' it in neutral cures. Removed the air filter which was toasted-no change. Cleaned throttle body with spray-no change. No vacuum leaks that I can detect..[always used the propane method] With dash lights that dim excessively with turning on the headlights and all the goofy electrical gremlins with these vehicles wiring harness, I'd not be surprised that it's an ecm thing. At hard braking at a traffic light the oil pressure takes its customary dive as rpm drops off-then motor stumbles as if trying to recover--could the oil pressure cutoff switch be reching its threshold and be sending eratic signal to the ecm??? Ever take a 350 v8 and dial the idle down to where ya could visually see the fan blades individually as they spin...My bets on the oil safety circuit........just a thought--what do you think V8Familyman? Any method to my madness?

Seems like you've thrown alot of money at ignition parts, granted you'll need em' sooner or later so a wise investmet. My 90 tbi does the same thing--runs fine--espesially cold [before closed loop] and then as ya hit a red light and stop the engine does the "I'm acting like I'm running outa gas thing" and stutters but doesnt stall--then tries to run at an idle only popin' it in neutral cures. Removed the air filter which was toasted-no change. Cleaned throttle body with spray-no change. No vacuum leaks that I can detect..[always used the propane method] With dash lights that dim excessively with turning on the headlights and all the goofy electrical gremlins with these vehicles wiring harness, I'd not be surprised that it's an ecm thing. At hard braking at a traffic light the oil pressure takes its customary dive as rpm drops off-then motor stumbles as if trying to recover--could the oil pressure cutoff switch be reching its threshold and be sending eratic signal to the ecm??? Ever take a 350 v8 and dial the idle down to where ya could visually see the fan blades individually as they spin...My bets on the oil safety circuit........just a thought--what do you think V8Familyman? Any method to my madness?