raymorton Posted March 4, 2009 Share Posted March 4, 2009 Hi guys, longtime comanche owner here... just absolutely love this little truck! I have a 89 4.0 that has so far ran like a watch... its amazing how much of it is original to this day, 250k later. Anyways, I have had a problem recently where the motor will warm up and do this really strange idle surging and will sometimes stall out but only when it comes to a stop like at a red light or something... here comes the interesting part- I got a thermostat for it about a week ago and advance sent me the wrong one and it was too late in the day for them to get one from the warehouse... rather than just put the old one back in, I simply just put the gasket on with no thermostat... problem went away! Next morning installed a superstat and felpro gasket and problem returns.. its definitely only when the motor gets hot which leads me to believe its possibly coolant temp sensor or an O2 sensor or some such. Going down the road its perfect, great power, no lag... just when the motor warms up you can't stop at a red light or anything without it flickering the oil light for a second and running rough, sometimes to the point of stalling. any thoughts? Link to comment Share on other sites More sharing options...
jtdesigns Posted March 4, 2009 Share Posted March 4, 2009 Sounds like the AIC or IAC,, yeah IAC.. http://info.rockauto.com/Airtex/Detail.html?2H1141.jpg Link to comment Share on other sites More sharing options...
maddzz1 Posted March 4, 2009 Share Posted March 4, 2009 I would check the IAC like jt said; but since it went away without a thermo you may be correct on the coolant temp sensor too. I would clean the iac first and if that don't fix it i would change the temp sensor since they are pretty cheap. The oil light flickering makes me think you have a Fram oil filter. If so, change with a non-fram filter and that problem should disappear. Link to comment Share on other sites More sharing options...
BLHTAZ Posted March 4, 2009 Share Posted March 4, 2009 The TPS would be a more primary concern for me in this scenario as well as the CTS (coolant temperature sensor). The IAC is most often associated with a high idle problem and not stalling...but, anything is possible. TPS test procedure is HERE CTS Test 1) Disconnect wire harness connector from CTS sensor. Test resistance of sensor with a high impedance digital ohmmeter. Resistance should be less than 1000 ohms with engine warm. The oil light flicker could be a sign of low oil pressure due to worn rod & main bearings or using a cheap / low quality oil filter like FRAM. Link to comment Share on other sites More sharing options...
raymorton Posted March 5, 2009 Author Share Posted March 5, 2009 hey guys... well i didn't get a chance to mess with it today, 2 emergencies out of town (I am in IT) so I will definitely try your suggestions. come to think of it, I do remember once seeing a recall on the TPS sensor which i think is original still... and I have gotten the problem where you start it and it revs like mad endlessly until i turn it off and wait a few minutes. anyways, will let you know what i find. Thanks again ! Link to comment Share on other sites More sharing options...
raymorton Posted March 10, 2009 Author Share Posted March 10, 2009 hey guys... today was comanche day =) hes fixed! I followed taz's deal for the tps first, its right up top and easy to get to... no dice it checked out perfect. I followed the procedures for the other sensors at this link- http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm O2 sensor showed absolutely no resistance, and the ceramic shaft turned independant of the nut... so I ordered a bosch from advance early in the day. Just for fun I wanted to see if the snap-on modis could get a function test or something up... to my great surprise it had a LIVE DATA STREAM for it... akin to a late OBD-1 vehicle, so before me was all the data I could ever need to know about it... coolant temp was reading correctly as was the MAP, vacuum was a bit low but you will have that on a car that old.I watched as the comanche heated up and started its normal "running fine" and then the thermo opened up and it went to drek.... well the scanner still read OPEN loop and the exhaust report was stuck on LEAN (while it clearly was running rich, could smell it) and the o2 voltage hovered around 4.7 and under load it went to maybe 3.9... totally wrong. Changed the o2 sensor out and the scanner switched from rich to lean on the exhaust back and forth, like all cars normally do, and the system went into closed loop and the problem vanished right then and there, even the idle surging was gone. As for the oil light flicker, I drained the oil and put in some fresh 20-40 with a K&N hp-2004 filter... and that problem was solved. Thanks again guys for all the suggestions. Link to comment Share on other sites More sharing options...
BLHTAZ Posted March 10, 2009 Share Posted March 10, 2009 Good job... :thumbsup: That is interesting info on the scanner Link to comment Share on other sites More sharing options...
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