ptcfast2 Posted August 6, 2011 Report Share Posted August 6, 2011 I've been having an issue with my 3.1 w/ RPM drops on deceleration/downshift. I finally figured out how to stop it from occurring by unplugging the EGR (the RPM drops would almost stall the car). I decided to get a new EGR just to rule that out and the new one didn't fix the problem. Lucky me! Does anyone know of any sensors that help the computer determine when to command the EGR open and closed? Any other ideas as to what would cause a problem like this (which seems to be caused by something related to the EGR)? Quote Link to comment Share on other sites More sharing options...
rjOlds Posted August 6, 2011 Report Share Posted August 6, 2011 Check that the Idle Air Control (IAC) valve is functioning properly, if stuck it could cause this, it needs to be able to open enough to allow enough air to increase the idle to prevent stalling. The shop manual lists a lot of stuff including the egr. - Vacuum leaks - ECM grounds may be poor - MAP sensor (assuming this is '93 or lower) - PNP (Park, Neutral Position) switch - throttle linkage sticking - IAC - EGR - A/C signal to ECM - Crankcase ventilation system (PCV valve) - Broken motor mounts Make sure the charging system is at least 9 volts and no more than 16 (should be around 13 when running) Then the typical plugs, wires, compression etc. This is the list in the order they gave. Based on the content I would take these as a semi decent list of most liekly to least, especially the stuff near the bottom which should be obvious as there would be other symptoms as well. For my money a vaccum leak or IAC seems like a good bet. Quote Link to comment Share on other sites More sharing options...
ptcfast2 Posted August 6, 2011 Author Report Share Posted August 6, 2011 It's a 98 actually. Wouldn't a vacuum leak cause the issue to show up with the EGR unplugged as well? Car runs perfect that way which confused me. Quote Link to comment Share on other sites More sharing options...
rjOlds Posted August 6, 2011 Report Share Posted August 6, 2011 Well I only have the manual for a '93 but a lot of that is still valid. I don't know if your engine has the IAC on it or not, but I would check and see. As far as a vacuum leak, it depends on where it is and how bad it is. Did you check to see if the egr tube or the opening was blocked with carbon? Someone correct me if I am wrong but if the EGR was disconnected (and I assume you meant electrically) the engine would not try and use it and would use different settings for the fuel/air mixture which may be why it helped. Now that it is connected again, it is trying to use it and if there is a blockage in the EGR system it might throw the ECM off enough to screw up things. Quote Link to comment Share on other sites More sharing options...
ptcfast2 Posted August 6, 2011 Author Report Share Posted August 6, 2011 Yeah, it's electrically disconnected. The whole engine has less than 4,000 miles on it....no carbon issues and most (if not all) of the sensors are new (excluding O2). It has an IAC valve as well from what I show. When I swapped it in it didn't have the problem for the first 2,000 or so. So I'm leaning towards a bad sensor, but not sure which one. Something to note though, the PCM thinks its controlling an L82 3.1...I swapped in an LG8 3.1. So that could also be contributing to my issues. Quote Link to comment Share on other sites More sharing options...
ptcfast2 Posted August 6, 2011 Author Report Share Posted August 6, 2011 (edited) Well here's another thing I just discovered: If I unplug the TPS and leave the EGR plugged in the issue does not occur. Edited August 7, 2011 by ptcfast2 Quote Link to comment Share on other sites More sharing options...
ptcfast2 Posted November 1, 2011 Author Report Share Posted November 1, 2011 Well, just following up here: The issue was a brake booster hose that was longer than the OEM one. Replaced it with a new OEM hose of the correct length and the issue went away. Funny how a few extra inches of hose caused this problem, but in hindsight it makes sense. Quote Link to comment Share on other sites More sharing options...
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