rough idle... suggestions?
Thread Starter
Instructor
Joined: Jun 2004
Posts: 234
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From: 1987- L98, auto OH
rough idle... suggestions?
Ok, I have a 1987 C4 with 49,000 miles on it and I have a "sometimes/most of the time" rough idle. It's not horrible, but is very annoying. So far, the following items have been replaced as part of my regular routine after I get a new car.
Distributor cap, rotor, plugs, wires, coil, air filter and fuel filter and oil change.
Sometimes you come to a stop light and it idles quite smooth, other times it seems rough.. not very consistent. I've tried a little fuel system cleaner in the tank, but no real change.
I am suspecting a few possibilities such as: O2 sensor, IAC valve, TPS or the like.
Anyone have any suggestions as to what to tackle first? Thanks in advance for any input.
Brad
Distributor cap, rotor, plugs, wires, coil, air filter and fuel filter and oil change.
Sometimes you come to a stop light and it idles quite smooth, other times it seems rough.. not very consistent. I've tried a little fuel system cleaner in the tank, but no real change.
I am suspecting a few possibilities such as: O2 sensor, IAC valve, TPS or the like.
Anyone have any suggestions as to what to tackle first? Thanks in advance for any input.
Brad
Burning Brakes
Joined: Aug 2001
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From: walled lake MI
i would start with cleaning (or replacing!) the IAC valve and cleaning the throttle body first. they are very accessible so IMO it's the "low hanging fruit."
if it is a flaky TPS the engine will not run right even at non-idle conditions. if it is a flaky O2 you will see it on the plugs or out your tailpipe.
fuel pump is another less-probable possibility.
if it is a flaky TPS the engine will not run right even at non-idle conditions. if it is a flaky O2 you will see it on the plugs or out your tailpipe.
fuel pump is another less-probable possibility.
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Originally Posted by tempest
i would start with cleaning (or replacing!) the IAC valve and cleaning the throttle body first. they are very accessible so IMO it's the "low hanging fruit."
if it is a flaky TPS the engine will not run right even at non-idle conditions. if it is a flaky O2 you will see it on the plugs or out your tailpipe.
fuel pump is another less-probable possibility.
if it is a flaky TPS the engine will not run right even at non-idle conditions. if it is a flaky O2 you will see it on the plugs or out your tailpipe.
fuel pump is another less-probable possibility.
with comments about IAC moter amd cleaning throttle body. but before I started throwing money into parts, get a shop with a good scanner to check out your car. This will give you a lot of info as to what is going on and point you in the right direction
Melting Slicks
Joined: Apr 2004
Posts: 3,287
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From: n/a SC
My 95 had a slighty rough idle about a year ago with only 29k miles on it took it to chevy they replaced 2 of the 3 o2 senors on it and thatmust have been the problem because it cured the idle.
I agree with the others now that I know more about these cars it could be your TB needing a cleaning.
I agree with the others now that I know more about these cars it could be your TB needing a cleaning.
Thread Starter
Instructor
Joined: Jun 2004
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From: 1987- L98, auto OH
Thanks guys! I appreciate your advice. Other than the very expensive dealer, there are no real good shops in our area that I would trust my car to. Really sad to say that! I have been threatening to clean out the TB, so will try that since it was on my "to do" list and will check out the IAC as well. Since the O2 sensor is cheap at AutoZone (about $20), I may just replace that as well. Again thanks! I'll let you all know what I find.
Brad
Brad
Thread Starter
Instructor
Joined: Jun 2004
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From: 1987- L98, auto OH
Well, I cleaned out the TB, what a mess! Never knew so much junk could be on the back side of a throttle valve! I also replaced the O2 sensor and it seems to run a bit better. The roughness is still there, so I'm going to clean the IAC next. What is the procedure for doing this? Is there a write-up on cleaning this thing? Thanks again!
Brad
Brad
Team Owner
Joined: Jul 2004
Posts: 28,422
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From: Hartford WI
Well, If you think the TB was dirty, you probably will get a shock when you take out the IAC. To clean that right, you would have to take out the TB and remove the 7 or 8 torx bolts holding down the IAC housing. Of course, the coolant hoses will have to be removed first. Then you clean the hell out of it with brake cleaner and reset the idle.
IMO, the best way to do it is to reassemble it and screw in or out the throttle stop screw till your scanner reads about 20-30 IAC counts. Then you reset the TPS and you are done.
IMO, the best way to do it is to reassemble it and screw in or out the throttle stop screw till your scanner reads about 20-30 IAC counts. Then you reset the TPS and you are done.
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Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
20 to 30 IAC counts is quite a bit with the a/c off. 9 or 12 is more realistic, but with a clean throttle body, you shouldn't need to adjust it anyway. In fact, if the plug is still covering the screw, I'd leave it alone, particularly given your low mileage. Do consider buying a scanner (and Shop Manual if you don't have it) - they're not that expensive and you can post any data stream you capture for addtional help.
Thread Starter
Instructor
Joined: Jun 2004
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From: 1987- L98, auto OH
Thanks guys! In regards to the scanner... do you have any recommended brands and good sources to buy them from? Sounds like this will be lots of fun! Also, any suggestions on a reasonable place to get the shop manual, or is Helms the only option? Thanks again.
Brad
Brad
Team Owner
Joined: Jan 2003
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From: Summerland B.C. Canada
Originally Posted by 1987C4
Thanks guys! In regards to the scanner... do you have any recommended brands and good sources to buy them from? Sounds like this will be lots of fun! Also, any suggestions on a reasonable place to get the shop manual, or is Helms the only option? Thanks again.
Brad
Brad
Helms prints G.M.'s shop manuals
Here are links for software.
http://www.moates.net/
http://www.ttspowersystems.com/DM_Beta_Software.htm
Check out ebay for a manual. Also the C4 parts for sale section of this and other forums.
Last edited by AGENT 86; Jul 29, 2004 at 09:13 AM.
Team Owner
Joined: Jul 2004
Posts: 28,422
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From: Hartford WI
Originally Posted by 1987C4
Thanks guys! In regards to the scanner... do you have any recommended brands and good sources to buy them from? Sounds like this will be lots of fun! Also, any suggestions on a reasonable place to get the shop manual, or is Helms the only option? Thanks again.
Brad
Brad
