Still chasing awful rough idle.....

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pippo

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Has anyone here with a 87 sunbird GT NON turbo, 2.0L, ever had a rough idle that is impossible to diagnose? No engine codes, new TPS, no vacuum leak that I can detect (tried all the methods out there), etc. Car idles rough, sometimes "hunts" which is usually a sign for a vac leak, and sometimes while at a stop, idle surges up to about 2000rpm, then comes down slowly to 1100.

Gees, Im at the end of the line. Are our sunbirds typical for bad IAC's, even when new or even when that check out for Ohms and cleaned out?

Also, maybe unrelated but the rough idle makes the entire dashboard shake like mad- glove box, radio slot, cluster gages, etc. Maybe I should check motor mounts?
Thanks, people!!
 
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So you haven't actually replace the IAC with a new one?
Have you cleaned the throttle body?
Checked the fuel pressure regulator vacuum line for gasoline?
 
Have you checked the MAS? little square thingy with a electrical plug and a vacumm hose... if the vacumm is cut or has a hole or cracked it wont function correctly.

Also, if automatic, did you try to disconnect the blue convertor lock up plug on the radiator side of the trans? (TCC)

Check the IAC port itself ( where the pintle goes into ) see if it isnt all coked up

Pcv hose is another idea it could be collapesed or bad pcv

Also the EGR could be bad , try disconecting the hose and plugging it.

Doug in P.R.:cool:
 
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melsg5 said:
So you haven't actually replace the IAC with a new one?
Have you cleaned the throttle body?
Checked the fuel pressure regulator vacuum line for gasoline?
Click to expand...

Thanks for the quick reply, Mel. Yes, i did put in a new one about 6 years ago hoping it would make a difference, but no such thing I wasted my $$.

But I read that even new ones can be bad. Only way to tell is to spec it out with Ohmmeter. I may try that tomorrow.......

Regarding fuel pressure, no, didnt check. I do have a fuel pressure guage- but before I get into a messy job I should explain that whenever I slam the pedal with RPM's over 3000, the car takes off like a ferrari, no sputter, no hesitation, no nothing, so should we suspect fuel pressure, Mel? Car runs BAD only during idle.

Throtttle body is clean. Sprayed it with cleaner a while ago- still no change.

Thanks!!
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92 Sunbird LE said:
Have you checked the MAS? little square thingy with a electrical plug and a vacumm hose... if the vacumm is cut or has a hole or cracked it wont function correctly.

Also, if automatic, did you try to disconnect the blue convertor lock up plug on the radiator side of the trans? (TCC)

Check the IAC port itself ( where the pintle goes into ) see if it isnt all coked up

Pcv hose is another idea it could be collapesed or bad pcv

Also the EGR could be bad , try disconecting the hose and plugging it.

Doug in P.R.:cool:
Click to expand...

Thanks again, Doug, for continued support. It is a manual (thats why it still runs after 30 years or so, hehe). I will inspect pintle port with light/mirror.

pcv hose is solid, but original. not collapsed. just changed pcv valve and no change. EGR: uh=ohhh, youre not gonna like me guys, here, but I disconnected that years ago. Why? Car runs soooo bad in ALL rpm's with it connected. Makes no sense to connect it back. Must be a bad egr but not worth buying new, I figure. I seriously doubt its the egr........

Thanks
 
Wouldn't hurt to try..............i remember having a 80 something Cavalier 2.0 that did the same thing....it was the IAC.

I remember on my current Sunbird had a low idle problem cleaned the IAC about 3 tiimes, ,cleaned the port that the IAC goes into, cleaned the throttle body and reset the computor a couple of times and it has been fine since.

Doug in P.R:cool:.
 
92 Sunbird LE said:
Wouldn't hurt to try..............i remember having a 80 something Cavalier 2.0 that did the same thing....it was the IAC.

I remember on my current Sunbird had a low idle problem cleaned the IAC about 3 tiimes, ,cleaned the port that the IAC goes into, cleaned the throttle body and reset the computor a couple of times and it has been fine since.

Doug in P.R:cool:.
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Good to know, Doug. Today, I yanked the IAC and washed it out with carb cleaner, then tested terminals 1+2, then 3+4, and got 55+ ohms, which is good. Shot cleaner in the port/bore, so thats clean now. Tested connector terminals for v and got 11+ v, but battery had only 9 or so- WEIRD. How could that be?? I poked/prodded at battery terminals but still got 9-10 v. Oh well, weirder things happen.

Anyway, started car, drove a bit, still same old problem. Sheesh.
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If your battery has low voltage or a bad cell (that would be about 10.0 V ) that can cause all kinds of drivability issues, and as the altinator should be putting out full voltage above 2000 rpm that may explain why the car runs well at higher rpms. How old are the Battery cables? Not a bad idea to change them if they over 10 years old.

I would double check the battery Voltage, clean both battery and chassis side conectors and check the engine ground straps and connections for corrosion. Before I bought any more parts.
 
cammerjeff said:
If your battery has low voltage or a bad cell (that would be about 10.0 V ) that can cause all kinds of drivability issues, and as the altinator should be putting out full voltage above 2000 rpm that may explain why the car runs well at higher rpms. How old are the Battery cables? Not a bad idea to change them if they over 10 years old.

I would double check the battery Voltage, clean both battery and chassis side conectors and check the engine ground straps and connections for corrosion. Before I bought any more parts.
Click to expand...

Thanks, Jeff. Good info/advice. Time to take a 2nd look at my battery, but have to say, when new, car ran the same. batt is from May 2009, car stil starts every day. Still, cant understand that goofy reading. Will report back here asap........
 
Rechecked my battery and its good- i inserted the probes DEEP past the rubber gromets, and hit the actual terminal bases. hard to explain, but previously, the terminal nubs (a tad rusty) showed way less than 12.4v. Battery is good. Cant trust those rusty terminal hex bolts, although, they do not interfere with v transmission.....
 
92 Sunbird LE said:
http://www.ehow.com/how_7959677_reset-baseline-idle-gm-tbi.html

Low fuel pressure can cause high idle also.................

Doug in P.R.:cool:
Click to expand...

Good link, Doug. I will keep that handy, and may even try it but I am afraid that if I lower the idle to 650, cart will srtall because remembner, it idles rough. Very rough. car shakes. Current idle is about 900-1100, depending on its mood. Maybe I ,mentioned it "hunts", varying from 1200, down to 900, like a see saw. Sometimes, 1600 down to 1300. Sheesh......

So, yes, idle is high but mostly upon initial startup which I understand is normal, based on Shop manual. Id comes down after a minute. Starts at 3000rpm, then subsides to say, 1000. Hate to mess with it and lower idle with rough idle condition., Im scared.
 
If you are still having the same issue of rough idle, go purchase new side mount battery terminal bolts. just use thumbs and push them out and same for back in. Can push against strut tower to get back in past hard rubber.
Doing that should cause you to keep battery disconnected for at least 15 minutes. That will reset your onboard computer. It will run rough a few moments as it goes thru learn program. Cant hurt anyway.
I can tell you it sounds like a vacuum leak to me. You can use parts cleaner to spray short blasts around vacuum lines and listen for change (momentary drop) in rpm. Do-not use wd40 its very flammable. Wear eye protection and a long sleeve shirt if you try this.
wouldn't hurt to have a water hose ready or a fire extinguisher close. Some spray cleaners are flammable as well. Read labels and choose one least likely to burn, heck even try water in a spray bottle.
I'll bet you will find one of those hard plastic lines that connect to a rubber elbow boot has broken off underneath the manifold or somewhere you cant see very easily.
These little Pontiacs run like swinger sewing machines if everything is right.
 
Roadking_ said:
If you are still having the same issue of rough idle, go purchase new side mount battery terminal bolts. just use thumbs and push them out and same for back in. Can push against strut tower to get back in past hard rubber.
Doing that should cause you to keep battery disconnected for at least 15 minutes. That will reset your onboard computer. It will run rough a few moments as it goes thru learn program. Cant hurt anyway.
I can tell you it sounds like a vacuum leak to me. You can use parts cleaner to spray short blasts around vacuum lines and listen for change (momentary drop) in rpm. Do-not use wd40 its very flammable. Wear eye protection and a long sleeve shirt if you try this.
wouldn't hurt to have a water hose ready or a fire extinguisher close. Some spray cleaners are flammable as well. Read labels and choose one least likely to burn, heck even try water in a spray bottle.
I'll bet you will find one of those hard plastic lines that connect to a rubber elbow boot has broken off underneath the manifold or somewhere you cant see very easily.
These little Pontiacs run like swinger sewing machines if everything is right.
Click to expand...

Thanks for the tips. Unfortunately I tried everything searching for vac leaks- even the stethescope method, which I found works best. Also, no loose elbow boots. Wish I had one loose though, would make it so easy!!

But why would new battery bolts help, if Im getting good voltage?
 
Sounded like in your prev post you may have some corrosion taking place? Anyway more than anything I wanted you to try the reset of your ECM. Worked for me. When I was having no start problems removing the terminals and waiting 15 or so would reset it and allow it to start. It runs awful rough for about 30 seconds as it relearns signals from the sensors then it will idle great just like it should.

I have removed and cleaned my connections and hope the ECM is good to go now. Fingers crossed X
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Ya know, Im gonna try it- got nothing to loose. Yes, these is some corrosion there. I might try new bolts too. Shouldnt be hard to find, hopefully.
I appreciate your concern.
 
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