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95 GP intermitant miss OBD1.5 question

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#41 matt1970



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Posted 28 May 2018 - 01:51 PM

Trucker,The rpms don't drop with engine temp if that's what you are thinking.At least 10 min or so before I shut it down.It may have a code but obd1.5 and no ses light coming on.I ordered an adapter for my scanner It should be in this weakened. No worries.I forget what engine I am working on all the time.Hard to keep track and gets worse with age Couldn't figure out why auto correct kept misspelling vacume. Apparently according to google I have been wrong for over 40 years!.You might appreciate the full story.

After getting the motor together I reached in and hit the key.As I am watching the motor run the RPM slowly climes to 4000RPM bouncing off the limiter.Of course at this moment the door swings shut with power locks engaged. I was distracted mid job and forgot to tighten the EGR bolts creating a major vacuum leak.I flooded the engine with throttle body cleaner to shut it down. Got the spare keys to get back in then tightened the EGR and restarted.the motor.It sputtered and coughed out the cleaner then ran good.Let it sit and idle up to temp,turned on the lights and AC.Idle dipped then stabilized immediately like it is supposed to.Shut it down and waited 15 min. Restarted fine.Drove around the the neighborhood for 15 min. of stop and go.all good.Let the engine completely cool overnight. Next day the RPM were at 2000 and it has no torque. It was working to clime a 5 deg incline hill at 60 mph.At one light had to keep my foot on brake and gas to keep it running.Now it is consistently idling too high when I start it.

 first thing I checked was vacuum leak. Carb cleaner and propane all over the plenum and clamped off vacuum ports one by one to eliminate a downstream vacuum leak.No change in rpm.Blocked off the EGR port to verify it wasn't stuck open.Cleaned carbon off the IAC pintel and seat. Verified it was actuating with the key. Now that I am thinking abought it there was no oring seal on the iac. Checked the MAP sensor again since I had to pull it off to check the vacuum lines under it.

 My plan is install an O ring on the IAC,see if the plugs tell me anything,reset the computer again.

#42 55trucker


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Posted 28 May 2018 - 02:00 PM

Well, if the O ring is indeed missing from the IAC housing that would be a source for a vacuum leak.






#43 matt1970



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Posted 31 May 2018 - 02:01 AM

knock on wood, fingers crossed, and trying not to jinx it, the beast lives! This car has always run a bit rough but back in February I gave it a tune up.After a few weeks it started missing after parked.Tested compression found a crack in #1 spark plug must have smacked it when installing #3.Replaced it and all was good for a few days.then it came back.Found a crack in #2.Must tweaked it when I pulled it out.40 years working on cars never broke a plug.I must be replaced it. All good for a few days.Found a crack in #4 and #6 was a little burnt so I replaced both..Ran too lean got hot and cracked..?? Ran good other than RPM issues. Then started missing again.#2 and #3 carbon trail and big old crack.Nope its the plugs!! Pulled all the autolites out, installed ac delcos and an O ring on the IAC. Still not perfect but better than it has ever sounded.While it was idling I unplugged the IAC  for a few seconds and RPMS are now holding at 1200. Unplugged the TPS for a few seconds now there is no hesitation in the throttle and idles smooth.This car never had a smooth idle! So major tune up,decarb,new seals,some preventative part replacement and get rid of defective junk plugs and it runs like a new (old) car.


Thanks to everyone for your help.If it acts up again I'm taking out to pasture and shooting it! lol


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