mx5mike Posted January 23, 2011 Report Share Posted January 23, 2011 I just aquired a 91 CS SL sedan 3.1 from my grandparents and there is a issue/'s that I am trying to solve. the car has seen limited use in the last 2-3 years and only tended to get driven a mile or 2 at a time to the store and back. the car has a slight what feels like misfire at idle but is totaly intermitant. Somtimes its steady and smooth somtimes slight stumble. also just recently its starting to feel like it is miss firing starting up a grade and just tipping into the throttle from a stop; and would somtimes hunt from 6-700 RPM to 1500 RPM coming to a stop from 55 on the freeway. if I put the car in neutral and then right back into drive it would go away to the next light. on the freeway at 70 on cruise and under WOT it runs great. I have changed the plugs (AC DELCO) and wires (Were the factory 185k mile wires (BOSCH)) did a over due oil change and changed the trans filter and fluid (Done within the last 50k), I also seafomed the intake through a vacum line and cleaned the IAC valve, its port in the throttlebody, and cleaned the throttle body. the IAC valve was caked in carbon and it doesn't hunt anymore but since I cleaned that the hesitation on throttle tip in is worse. all the vacum lines are good and I can't find any leaks in the system with the carb cleaner method. I am going to do a fuel filter tomorow but grandpa said its been done in the last 10 to 15k miles. Could this be a Dirty MAP Sensor? how would/can you clean it, It seem's to be a sealed unit. I plan on doing the O2 sensor in the near future, and will do it now if somone thinks it could be causing the issue at hand. I am not getting any codes or check engine light. What do you guys think? TIA Quote Link to comment Share on other sites More sharing options...
AL Posted January 23, 2011 Report Share Posted January 23, 2011 Icm... Its mounted under your coils Quote Link to comment Share on other sites More sharing options...
mx5mike Posted January 23, 2011 Author Report Share Posted January 23, 2011 Ok I will look into that. I am going to replace the O2 Sensor and fuel filter today, and see what if anything that changes. Is there a way to clean a map sensor? Quote Link to comment Share on other sites More sharing options...
BXX Posted January 23, 2011 Report Share Posted January 23, 2011 Sounds like a sticking EGR. Quote Link to comment Share on other sites More sharing options...
AL Posted January 25, 2011 Report Share Posted January 25, 2011 There isn't really a way to clean it Quote Link to comment Share on other sites More sharing options...
mra32 Posted January 25, 2011 Report Share Posted January 25, 2011 if you have a multimeter, you can backprobe the sensor connector and verify its operation with readings when the key is on, engine off and then at idle. I might be thinking of TPS readings, but i think its like .16V on the map sensor when its at atmospheric (engine off) and somewhere around 4V when the engine is at at high vacuum (engine idling). Multimeters are like $3 at harbor freight Quote Link to comment Share on other sites More sharing options...
mx5mike Posted January 27, 2011 Author Report Share Posted January 27, 2011 Thanks for all the help. I have checked sensors and everything checked out. I have run 3 tanks of Chevron Premium with techron through it and it is getting better and better with every passing mile. I have also been driving it fairly hard to try to get the carbon cleaned out. I think there was an injector gummed up or somthing cause after some high grade gas it doesnt hiccup hardly at all anymore. I will keep everyone posted as to how it goes in the next couple of tanks. Quote Link to comment Share on other sites More sharing options...
mx5mike Posted January 30, 2011 Author Report Share Posted January 30, 2011 ok a bit of an update. things are not great. I finaly replaced the fuel filter and changed the vacum lines as some were questionable. it still has a hesitation under light cruise and idle. I am at a loss of where to look next. Gas mileage is also off by quite a bit. I do 90% highway at 70 with the cruise set and am only getting 19-21. When I took this car on a 500 mile round trip a few years ago we got 31 MPG and that included dealing with traffic in downtown Seattle. what the heck is going on here. I have looked through the factory service manuals and can seem to find anything. Please help before I pull out my hair. Quote Link to comment Share on other sites More sharing options...
threepointone Posted January 31, 2011 Report Share Posted January 31, 2011 my 3.1 lumina does the same thing only has hesitation until it warms up then it goes away Quote Link to comment Share on other sites More sharing options...
mra32 Posted January 31, 2011 Report Share Posted January 31, 2011 (edited) ok a bit of an update. things are not great. I finaly replaced the fuel filter and changed the vacum lines as some were questionable. it still has a hesitation under light cruise and idle. I am at a loss of where to look next. Gas mileage is also off by quite a bit. I do 90% highway at 70 with the cruise set and am only getting 19-21. When I took this car on a 500 mile round trip a few years ago we got 31 MPG and that included dealing with traffic in downtown Seattle. what the heck is going on here. I have looked through the factory service manuals and can seem to find anything. Please help before I pull out my hair. This sounds pretty similar to mine. The thing that bothers me the most is the shit idle, but I'm getting 18.5 mpg these days. It seems to be getting worse, but I'm only comparing to the summer when it seemed to be running worse and getting around 23 tops. At this point I have verified correct operation of every sensor, replaced the O2 sensor, inspected and regapped spark plugs, verified cylinder compression within spec, replaced spark plug wires, verified correct fuel pressure, seafoamed, cleaned the IAC, cleaned the EGR, replaced dubious plenum gaskets, checked vacuum on the plenum while running. I most of the stuff I did is documented in a thread on here. I might rewire the O2 sensor lead for shiggles, due to there being weird routing of the wire and it seems like there is way too much wire. I'll make sure the computer is plugged in well since a few years ago I had to replace it and I might have messed up the clips on the connectors. Similarly, I'll likely redo the engine grounds, since I can see the copper wire and there is oil and dirt between the individual strands. I got an extra set of injectors that have proper impedance, so one day when I have alot of daylight, its not too cold or snowy, and I can afford to not have my car for a few days given I royally screw something up, I'll pull off the plenum and mess around with that. Beyond that, I'll replace the ICM and coil packs, since I'm fairly certain I could use a new coil or two at this point. In all reality, I should have done ICM and coil pack first, but when I did most of this work, I was not working, so I had no money and nothing but time, so I did the stuff I could check with my tools. Now the opposite is true. The remaining stuff not only takes money but time. Edited February 1, 2011 by mra32 Quote Link to comment Share on other sites More sharing options...
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