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95 burb.... considers napping randomly at stop lights [Expired Topic]

3707 Views 15 Replies 6 Participants Last post by  unplugged
My 95 has just recently started to sputter and rough idle when I get to intersections, I haven't noticed any problems when the gas is applied. It hasn't died completely yet but randomly as I slow/stop at an intersection it starts to sputter out and sounds like it could actually stop. As soon as it gets some gas its fine again. I changed out the plugs, wires, cap, rotor last week with no change. It seems to be getting a little worse every couple days. Happens about 3 times a day while driving around town. Any thoughts? I dumped some injector cleaner in this morning thinking they might be a little clogged up......
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Kinda sounds like a vacuum leak or an IAC valve that is not responding the way it should. Those throttle bodies were known for having a vacuum leak under the throttle body, the gasket between the TB and the intake gets real brittle with old age and creates a vacuum leak that is real hard to find.
Is this only when at idle? It drives normally at driving speeds as far as you know?
That's exactly what my dad's 94 was doing. It turned out to be the a/c compressor trying to take a dump. Turn off your a/c and see if it smoothes out. If so, that would be the problem.
This does only happen at stops, on the road when gas is applied it runs fine. The AC is off now that is a whole additional issue, I need to replace the whole front end of the AC. Its at a shop now getting checked out, I was out of ideas and time. I will let you know how it turns out.
Just got a call back from the shop, they said that at the intersections the timing is getting set back to about 2 degrees where it would normally be at 17 degrees. The shop manual says the only thing that impacts the timing lke that is the ignition module and they put a new one in and nothing changed so they took it out.

Picking up the truck in an hour, they give up ;-)
I thought the computer controlled timing, not the ignition module. Is the check engine light coming on?
There are no check engine lights and the computer has no maintenance codes either active or in the recent history.
Honestly though the problem is not solved, I have replaced the plugs, wires, cap, rotor, ignition module, Battery and still intermittantly when I some to an intersection or more generally remove my foot from the accelorator the truck partially stalls. One of the shops that looked at it said that at the point is stalls the alternator meter dips and the timimg drops from 17 degrees to 2 degrees. On a couple of occasions the truck has actually stalled completely. My only other thought on this is the fuel pump.....

Anybody else have an idea?
Nice new GMC!!

The only other thought that comes to mind on your 95 is possibly the torque converter clutch is not releasing immediately when you come to a stop. I'm not sure if that would set a code on the obdI systems (which the 95 is) but it does on the obdII systems.
I will have to look into that one. Has anybody had any experience with the throttle postion sensor? How to check it or replace it etc...? A guy here at the office suggested that might also be a culprit for something like this.
another thing somebody mentioned is the IAC (Idle Air Controller).
if you have an EGR valve on intake it could be getting stuck open from carbon decarb motor an check or change egr valve johnny
Ooooh, I love the intermittent or difficult to trace troubles. Especially when they aren't on my truck. lol. Sorry, but my first two stops would be:
1. Check for vacume leaks
2. Check the fuel pump pressure.

To check for a vacume leak I'd remove the air cleaner/inlet assembly off the throttle body, then with the engine at idle I'd start to cover the air inlet on the TBI unit. As you start to 'choke off' the air supply if the engine starts to idle faster, or if a rough idle smooths out I'd suspect a vacume leak. Get a spray bottle filled with water and spray it around the gasket surfaces, like the throttle body gasket, the intake gasket area etc. Spray around the throttle body shaft too. If the idle behaves like it did when you were 'choking' the engine that is the leak source.

I had a dodge that had stalling stumbling problems that were so intermittent that it drove me almost to drink. I bought a fuel pressure gauge and spliced it into the fuel line. I ran the hoses to the gauge mounted in that area between the hood and wipers. (Don't try running into the passenger compartment. Big fire hazard.) Sure enough whenever the old dodge starting stalling the fuel pressure dropped to the 5-8 psi range which was too low. Replaced the fuel filter and the electric pump that was in the tank and the problem was gone.

With a jury rigged fuel pressure gauge, you'd get an idea what the fuel pressure was at the time the symptom was occuring.

Just my first crack at this one. Please keep us informed. Like I said, I really love the tough ones.......
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