Guest BAABUICK Posted November 24, 2009 Share Posted November 24, 2009 Hi everyone,I have an '89 that does not idle smoothly when stopped in gear. For instance, when waiting at a red light, RPM'S will quickly fluctuate from 650 to 600 back up to 650 resulting in a bit of a shudder that lasts about a second. Over time it seems to be getting progressively worse.Conditions:Very smooth idle @ 750 RPM when in Park/Neutral RPM'S drop to 650 when in gearFuel system has recently been treated (problem existed before treatment)Battery & charging system are goodOther than this little hiccup, car runs & performs excellent Dirty IAC? Dirty MAF?Any suggestions are appreciated!Thanks in advance,Brent Link to comment Share on other sites More sharing options...
BrentS Posted November 24, 2009 Share Posted November 24, 2009 Not sure about other owners, but my '89 doesn't run really smooth, either. But, I think it runs "Reatta normal". Mine goes up and down 50, maybe 75 rpm when idling.p.s. Nice name Brent Link to comment Share on other sites More sharing options...
Guest mongeonman Posted November 24, 2009 Share Posted November 24, 2009 Mine too. Link to comment Share on other sites More sharing options...
padgett Posted November 25, 2009 Share Posted November 25, 2009 Classic signs of a dirty IAC. Bad ones will stall when coming to a stop and be hard starting also. Link to comment Share on other sites More sharing options...
KDirk Posted November 25, 2009 Share Posted November 25, 2009 Judging by the tach on my car, at idle it runs 600-650 (warm engine), and routinely fluctuates 25-50 RPM's but does not cause any apparent roughness that I can feel. I always thought this was normal - even my 95 Deville varies up to 50 RPMs at idle, usually in a range of 575-625. I've not seen an engine that can maintain dead-on idle with no variance at all. Note that my IAC has been thoroughly cleaned, and made no difference in this regard. Bear in mind also that the ECM output scales the engine speed reading to have a minimum resolution of 25 units, meaning that it will round up or down to the nearest multiple of 25 on the display, so the actual variance may not be as much as it "looks" like on the gauge. It may be that the slight change in RPMs is not an indication of the underlying problem causing the rough idle. The IAC is a good first place to check, although a fouled spark plug, failing injector or any number of other ignition system issues could be at play. KDirk Link to comment Share on other sites More sharing options...
D-a-n-i-e-l Posted November 25, 2009 Share Posted November 25, 2009 Also bad O2 can cause the issue also. If it has not been change in 20-30k I would do it. It is regular maint. Link to comment Share on other sites More sharing options...
padgett Posted November 25, 2009 Share Posted November 25, 2009 Mine has always been very smooth but then I also kicked the idle up to 700 rpm to improve the a/c at stoplights. Very low idle speed is an indicator of either a ded cam or VVT. Link to comment Share on other sites More sharing options...
Guest BAABUICK Posted November 25, 2009 Share Posted November 25, 2009 Mine has always been very smooth but then I also kicked the idle up to 700 rpm to improve the a/c at stoplights. Very low idle speed is an indicator of either a ded cam or VVT.I have always thought to myself "If only I could bump up the RPM's a little bit...". How can I do this?In the meantime, I will clean both the IAC & MAF (probably long overdue anyway) & will report back any improvement.Thanks to everyone for your input! Link to comment Share on other sites More sharing options...
padgett Posted November 27, 2009 Share Posted November 27, 2009 Same time I reprogrammed the PROM to turn the fans on earlier. Is just a set of bytes. Link to comment Share on other sites More sharing options...
Guest BAABUICK Posted December 19, 2009 Share Posted December 19, 2009 Classic signs of a dirty IAC. Bad ones will stall when coming to a stop and be hard starting also. UPDATE...Finally had a chance to clean the IAC today & now she purrs like a kitten.Thanks Padgett! Link to comment Share on other sites More sharing options...
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