I heard my 1987 sunbird GT (non turbo) has a vacuum advance in the module (distributor module??). And that this can affect the engine idle smoothness. Is that true? I own both a Haynes manual and the official Shop Manual which is extensive, and i never found any such thing in there. And regarding troubleshooting for rough idle, no such mention ion all the checks listed in the shop manual.

Thanks!

I don't think so. I looked for one at parts sites and none showed one. I did see the distributor and it doesn't appear to use a vacuum canister. Is there a vacuum line going to the distributor?
I would too would think something like a vacuum advance system would be mentioned in the service manual.

Can you share your engine specs.Just a 4 or 6 and throttle body or multiport.Also please describe the issue your car is showing.With this I could elaborate some things to check to isolate the problem.

Thanks, Butch and Ron! Yes, I also do not believe my car has it- there is NO tubing attached to the distributor base, nor anywhere near it. Also, Over the last 24 hours, I read extensively my service manual (a real one from Pontiac), and no such mention anywhere, just the HEI ignition with distributor.

So, What Im after is locating a suspect vac leak. My car (Im original owner!) has rough idle, has had it for past 14 or so years. I checked allover the place but couldnt locate any leak. I suspect a vac leak cuz only at idle do I get rough running/stumbling, but when I drive all is fine, and ever when I floor the pedal and observing the tach, it passes 4000, 5000 rpm with NO hesitation, NO stumbling at all. Accelerated great for a non turbo, single TBI.

Oh- 4 cylinder, 2L. Non turbo, like I said.

Thanks!

Wanted to add/edit my above post but see no edit button. Anyway, I should add that there are no codes stored in computer. Over the years I have changed out the AIC, and TPS. New injector, although, never needed it, it was a faulty diagnosis by the Dealer (and cost me $$$ for nothing, and never fixed the problem).

I am convinced it is an elusive vac leak. OR if not, something that appears to be a vac leak like bad valve/valve spring/etc.

just put a vac gauge on it and needle vibrates between 19-20 " mercury. I floor it and it jumps to zero then quickly back to around 19-20, then vibrates again.

Should be dead steady, right? Also, with engine at say, 3000rpm steady, needle holds extremely steady.

The best way I have found to find a vacuum leak is a smoke test.
I bought a small 120v air pump that I put a cigar in and let it blow the smoke into the intake via a vacuum line. If there is a leak, you'll see the smoke escape from it. Works like a charm and cost less than $20.00, including two cheap cigars. Only took about a 1/3 of one of the cigars to find the leak. They'll burn up fast, but once the smoke gets pumped into the engine, it begins to come out in short order. And, it is a tool that can be used over and over again when needed. Be sure to seal off the air intake so as to not allow much of the smoke to come out there.

My leak was the hose that goes to the MAP sensor. It was one size too large.
Here is the thread with what I used. Just scroll down a bit. Also the last post in the thread is interesting in what the OP found to be his idle problem.
http://www.v6z24.com/jbodyforum/intermitent-high-idle-problem-not-vacuum-leak-t131282.html

You can find videos on doing smoke test vacuum leak on YouTube.

Good luck

Good tip, Butch. Worth a try. I shouyld also mention that for years the EGR has been disconnected with tube pluged up with a stopper because with egr connected the car ran like absolute hell. Matbe this is a sign of a vac leak??

Anyway, I will try this maybe later today. Geez, where do you buy cigars???????Never bought one. Grocery store? LOL

I think I got them at a convenience store at the counter. Just tell them you want the cheapest single ones they have. Less than a buck apiece, I think.

The egr vacuum tee'd off is a major (BAD)!!!!!!!! This creates the same problem if the egr diaphragm was to lose vacuum or be stuck in a closed position..UNplug the tee and see if this clears up the problem.If the problem goes away the EGR is sucking air due to age and not holding vacuum.I will not say that the map sensor is not at fault however,the EGR would be my primary focus until you report back with the vacuum line unblocked and drive and see if the issue goes away!!!!The vac line unhooked will not hurt anything just a slight mpg adjust lower but,no big deal.I will share a link to check your map sensor Tuesday as it is late and I am tired.

Sorry for delay, Butch, but I will follow up with you as I think you offer good advice! Yeah, EGR needs attention. Hope this can wait cuz I have to go out of town for maybe 2 weeks. Hate to put it off but have no choice. I WILL get back to you, promise Dont forget about me!!!!!

no quacks wrote:Sorry for delay, Butch, but I will follow up with you as I think you offer good advice! Yeah, EGR needs attention. Hope this can wait cuz I have to go out of town for maybe 2 weeks. Hate to put it off but have no choice. I WILL get back to you, promise Dont forget about me!!!!!

OOps, I assumed the last post replying to mine was from Butch and not Ron. Sorry Ron- I should have addressed to you, although Butch also has been helping. Didnt meant any harm........

No problem it happens.Either way I am sure we as a group can narrow down the problem and be cost saving!

No it don't its computer controlled. If by some crazy chance I'm wrong. If it does there would be a round bulb ? On the distributor with a vacuum hose going to it

Back from my trip. Gonna try the smoke test before messing with the EGR. Should I keep the air filter housing on/intact? I will seal of the large intake though......I guess doing a smoke test with air filter and housing off defeats the purpose, right, as the vac leak could be from there as well?

Wow, that smoke idea works! Should have done it years ago! But Im not so convinced yet thats my problem as I have seen this hope before and it went up in smoke(hehe). Smoke was seeping out from below the air filter housing, but impossible to see cuz its underneath. But when I removed the steel housing I did notice the round seal/gasket was kinked/crushed at one spot. Gotta be the source. Ordered a new one and will try it again tomorrow.

no quacks wrote:Wow, that smoke idea works! Should have done it years ago! But Im not so convinced yet thats my problem as I have seen this hope before and it went up in smoke(hehe). Smoke was seeping out from below the air filter housing, but impossible to see cuz its underneath. But when I removed the steel housing I did notice the round seal/gasket was kinked/crushed at one spot. Gotta be the source. Ordered a new one and will try it again tomorrow.

A leak before the throttle body has no effect on a jbody as they are not mass air flow cars. The few first gens that were gm disabled the sensors so even if your car had one it wouldn't matter. If you have a vaccum leak it has to be part of the engine.




On the inside my car looks like a fighter jet.

Wow, thanks Rob- I didnt know. I just wasted some $ and time on a new seal. Oh well. you learn, not big $$$ anyway. But today, Ive got bigger problems, which I will explain in my new thread coming up about my EGR valve disaster.......