Intermittent surging/ rough idle - '90 GW

[AM Woody]

Greetings, looking for some advice on the wife’s ’90 GW. Has 140K on it, always ran good over last 2.5 years and 20K miles. Couple weeks ago experienced a rough idle now and then, and a couple times it stalled at idle and when I restarted it, it idled smoothly. Then on two occasions on the highway when giving it gas, there was a hesitation. Changed the fuel filter, it behaved for a week or two. Drove it Friday nite four miles on the expressway, got off and it started surging and hesistating, and idling poorly. Drove home 4 hours later, ran okay, idle a little rough.

Yesterday, I checked over vacuum lines, etc. Was still idling a little rough, I sprayed a bunch of carb cleaner in the carb, and it seemed to smooth out. Raised the idle a bit (which I’ve done in the winter before) and it was running good. Went for a test drive, idle still a bit rough. I floored it and let it go through the gears and it smoothed out. Drove it @20 miles last nite out to dinner and visit the in-laws. Ran great and idled smoothly all evening, city and highway driving.

Today, the wife drove it about four miles up the expressway, and when she slowed down, it started surging and hesitating like it had done for me, and it’s idling poorly again.

Can’t help but think it’s carb (or fuel (or vacuum)) related. Replaced carb last year with a clean-looking used “factory rebuilt by Holley” carb that was on my parts truck. Didn’t do anything to it but change the power valve. Passed emissions last fall. We dropped and cleaned out the tank about two years ago, and replaced the sender, etc. Pulls 20” steady vacuum when idling smooth, will erratically drop 1-3” when idling rough.

Any thoughts? Maybe dirty jets, or a needle or something is hanging up in the carb? Fuel pump going out? I hate these intermittent problems. Sorry for the long post. Any advice appreciated.

Andy

[leila]

Just a thought...check your egr valve. It may be sticking.

[oddfire]

sounds like its time for plugs,cap and rotor....phil

[TexasJ10]

Something similar happened to me once. The carb mounting nuts had gotten a little loose. Once I snugged them, the problem went away.

[AM Woody]

Thanks, I will check the EGR. I forgot about that and did read it can cause weird problems. Will check mtg. nuts, too, as I've had the carb off a couple times in the past. I did spray carb cleaner around the base gasket to try to detect vacuum leaks. I did notice the dist cap contacts are pretty tracked up and I've never put plugs in it. I did decide I will give it a tuneup for a baseline, but when it's not acting up it runs very smooth. I agree the cap, rotor and plugs will affect idle, but when this surging started it was pretty severe, making the truck buck quite a bit. I think it's something more... Thanks again...

[mountaincrusher]

another culprit could be the base gasket, could be leaking some.sorry not much more help, but rough idle and hesitation could be many different things besides carb.

[Dan]

Definitely check the EGR. Also, if you haven't changed your plugs/cap/rotor, I would do that. Those symptoms could be caused by poor ignition parts too. Couldn't hurt, you probably need it anyways, and the cost is low. Maybe it would even be a good time for the TFI upgrade.

[kidatforty]

After checking all the other things mentioned and still lousy, pull vac hoses off carb. one at a time and apply vacuum to find leaks. (crummy diaphragms, etc..)

[AM Woody]

Looks like the EGR valve is stuck. I'm going to go get one. Those two rusty Torx bolts don't look like very much fun. Should I run the engine to heat them up? Thanks.

Andy

[M/Z]

I had the excact same problem for the last couple of weeks. I replaced the distributor cap, the rotor and the spark plug wires. On every vehicle I've owned, this problem has always turned out to be the spark plug wires. Don't bother trying to figure out which wire is bad, just replace the whole set. It's easy, relatively cheap and will eliminate that as a potential problem. Yes I've had simular symtoms that turned out to be vacum or carb, but the intermitent frequency of the surging would point right to plug wires. Hope this helps.

[jeepguzzi]

Chi-Town90, You aren't the red Grand Wagoneer that I've been seeing, are you? Saw one at Portillo's and then a week later, I saw one at California Pizza Kitchen. (I eat good when the in-laws are buying!!)

[AM Woody]

No, jeepguzzi, our '90 is gray with dead clearcoat. Usually driven near downtown by a cute brunette (my wife.) We do occasionally venture out to the 'burbs with it.

Anyhoo, EGR on order for tomorrow. Been reading the manuals - cold drivability seems to be suffering, too, so I hope that's it. Will pick up tune up parts, too. Hopefully I can wait on those until the weather breaks...

Thanks for the additional advice.

[ January 13, 2003, 03:24 PM: Message edited by: Chi-town90 ]

[reddog]

If the EGR isn't the problem trace those vacuum lines. Sounds like vacuum leaking intermittantly.

Kerry