Hairline crack in one spark plug most likely
This smacks of a dirty/sludged up automatic idle speed control system, but it could also be due to other faults. I suggest you 1st run a OBD1 fault code test on the ECM of the engine, the test can been done without a scanner by following the easy instructions at this link, the fault code definition's are there as well, here is the link to the test procedure: http://www.extreme-check-engine-light-codes.com/GM%20OBD1%20Decoder.htm Get a can of throttle valve cleaner (it is made by CRC) from the local auto parts store, spray it into the air intake of the engine until you have used about half the can, you will need to hold the idle up while you do this, it will try to stall, after this shut the engine down and disconnect the Negative (-) battery cable for 5 minutes. The intake is now clean, if you continue to have the idle speeds problems you may need to seek the help of a professional to test the system further.
To deal with the idle surging up and down do the following procedure to clean the throttle valve and automatic idle speed control valve:
You were so adamant that you did all the install of new parts and reconnection of secondary wiring correctly and had made no mistakes that I left that alone as far as a cause. Some folks get really upset when I suggest they did the job wrong Glad you found your mistake. I still recommend you clean the idle speed control system as a part of your regular maintenance. emissionwiz
You said you found the problem and it was fixed so I am a little confused here, could you please inform me if you have or haven't?. The test plug to run the test is under the dash in front of the drivers seat, just use a paper clip to jump the terminals, run the test just to rule out any fault codes in memory.
If my assistance with this problem has proved useful to you could you please rate the solution as "HELPFUL" for Fixya.com, this is how I am compensated for my time and expertise ($4.00). Thanks!
×
With the items you have changed, I am assuming that all is well with them since they are new. I am looking at the Idle Air Control valve as one of the culprit since the symptoms are there, which is rough idling. It may not be bad, probably just needs cleaning.
http://www.partsgeek.com/mmparts/idle_control_valve/chevrolet/k1500_suburban.html
It should be located near the intake manifold. Above has a sample on how it looks like. Other issues could be loose ground or loose wiring or vacuum hoses that may have worn out or loose.
If you have carb cleaner, try spraying it on the intake manifold to clean out the MAF.
If you cam, try to have a scanner connected and see if you can retrieve errors from the computer box. Some shops would let you borrow them. The errors should help you accurately identify the problem.
This may seem odd but the idea of an idle control vale or a MAP sensor seems to be in the air. I would test these two sensors and see what comes up. you may even get a check engine light if it get bad enough. Regardless that's where I would start.
hehe, I have done similar things in the past, I don't think I would have seen that coming. Glad you fixed the problem!
×
132 views
Usually answered in minutes!
After just putting in plugs, how then all of a sudden does the engine idle get rough and surge, whereas it wasn`t doing so before?
Pure co-incidence? Or did the MAP sensor and/or idle control valve just happen to time things that way?
Looking forward to the reply
Found the problem.......Checked everything again today. The short plug wire going from the distributor to the coil was improperly reversed and the shorter rubber nipple was put on the coil instead of on the distributor. As a result, the plug wire loosened from the coil a little causing the intermittent rough idle ans surging.
Runs great now!
Thnx for the help.
Emission Wiz,
Thanks for your input. Reviewed the link you sent regarding running the OBD1 test on the ECM. On the right side of that page it basically says to run this test "after" seeing a warning indicator of some kind on the dash. Presently, there are no warning indicators such as "service engine soon",,"check engine",,,or anything else. That`s telling me that there are no trouble codes evident at this time to retrieve. And just in case I need to perform this test at a later time, where do I find that adapter it refers to?
First, I`ll try the simplest course of action first and get a can of that throttle body spray you suggest.
Thanks,
John
Thought that I did solve the problem with that loose plug wire connection, but it did not last long. At your suggestion, completed the throttle body spray down and removed the negative battery cable for about 5 minutes this morning.
As before and now, there are no warning indicator lights on in the dash.
The idle problem increased with far more frequency after the new set of plugs were installed. So I`m installing another set of AC/Delco plugs today. There could be a hairline crack of some kind in one of them.
If this 2nd set of plugs still doesn`t solve the issue, I`ll run that OBD1 test that you suggested.
Thanks again
Put in another set of spark plugs yesterday and the idle problem has now been solved.....Apparently (guessing), some very small amounts of graphite thread grease used for each plug (for the first set installed) got onto some the the electrodes which affected the combustion process. Didn`t use any thread grease for the second set.
Idles just fine now and the truck runs great.
Problem now solved. Along with a complete throttle body cleaning as you suggested, I put in another set of plugs yesterday and the idle is now fine. Test drove the truck many miles around town and on the freeways to make sure.
My guess, is that there were very small amounts of thread grease which somehow got onto or near the electrodes, which affected the combustion process in one or more of the combustion chambers. Didn`t use ANY thread grease for the second set of plugs.
As it turned out, it was a problem which I caused requiring my extra labor and expense for new plugs to fix.
×