Chrysler Repair: 97 2.5L V-6 rough idle, intake manifold gasket, upper intake manifold

Question
QUESTION: Hi.  

Background: 1997 Sebring convertible JXI. 2.5L. This project started with a leaking radiator.  I replaced the radiator and the next logical thing happened, another leak.  It appeared to be at the water “inlet” tube behind the thermostat.  As you know, that is a difficult area to see what exactly is going on with the engine assembled, so I replaced all the gaskets and seals in the thermostat housing.  No leaks.  Also, I took advantage and replaced the spark plugs while the upper intake manifold was off.  Now, I’m having an issue with the car running properly.  Prior to replacing the radiator the car was running well.

Previous symptoms: (before troubleshooting) Car would start and run perfectly until at operating temperature.  After operating temperature is reached it will “miss” on the idle at around 700-800 RPM.  It will rev up and run fine at all other RPMs.  The engine was not overheating.  The more load that is on the engine, the worse it “misses”.  It was not drivable.  I got various sensor engine codes and have replaced sensors and/or cleared the codes.

Current symptoms: I have gotten to the point where the car is now drivable (much, much better than it was).  However, it will still “miss” when idle with a load as described. Another symptom is that when the throttle body is opened quickly the car wants to die (likely running lean).  The throttle body must be closed rapidly and then the computer corrects.  I can ramp up the throttle rapidly but not “punch it” without stalling.


I have replaced in this order:

Spark Plugs (original Bosch, have since changed to Champ. Dbl Plat.)

Spark Plug wires

Distributor cap

Distributor rotor

MAP sensor (got code from key check)

EGR valve

Upper intake manifold gasket (twice)

EGR solenoid valve vacuum tube (from rear of manifold, was brittle and broke)

IAV: The IAV port was heavily covered with carbon as was the plunger.  I cleaned the carbon on the port and ultimately broke the IAV and replaced it.  The connection between the EGR tube and the upper manifold was heavy with carbon and I cleaned it.

Fuel filter (was unlikely cause but worth a shot)

IAT sensor (was getting error P0113 after cleaning off carbon)

Coolant temperature sensor (no code but learned the computer uses this information AND the IAT information to calculate air flow)

The car began running much better at this point as described.

I have checked:

Vacuum, and apparently no leaks.  It pulls 18.5 inches of vacuum and if I disconnect a hose the sucking sound is audible.  No fluctuations with my meter (analog).

Intake manifold gasket leak.  I did this with carburetor cleaner as far around as possible.  No pick up in engine RPMs.  I can try with propane but I don’t believe it to be a vacuum leak.

Visible check of all fittings, hoses, and connectors and they all seem good.

I confirmed timing, Cylinder 1 TDC with rotor position.  

I have verified 5VDC to the MAP, IAT, and TP sensors.  I have confirmed continuity to the various pins for the IAT and TP sensors as previously mentioned in some of your previous posts.

I am thinking this is a throttle body position sensor error.

Any other suggestions?  Any help is appreciated.  Thanks!


ANSWER: Hi Darren,
I am truly impressed, not only with what you have reported you have done but also the quality of the report itself. Would you like to sign on as an "expert" at the site?
As I was following along, each time I thought of something, sure enough you had done it!
I agree with the idea of a slight discontinuity of the TPS variable resistor/wiper interface. You can test that by measuring the voltage with the ignition in 'run' on the center wire while you slowly move the throttle from closed to wide open. The voltage should range smoothly from more than 0.6 to less than 4.5V
I am not familiar with the term IAV but I assume that is the idle air control motor. I also assume that you cleaned the throat and both sides of the the throttle plate.
I will keep your question highlighted as a prime example of what to look for when a problem like this occurs on the 2.5.
Please let me know if the TPS discontinuity theory works out.
Roland


---------- FOLLOW-UP ----------

QUESTION: Roland.  

Thanks for the prompt response and thanks for the complements.  Indeed the IAV, as I have heard, stands for Idle Air Valve.  I spent a lot of time researching possible issues and tried to resolve before involving anyone else.  My “expertise” as you have put it only exists because of people like you that try to assist without gouging the unfamiliar.  

As far as helping out as an expert, that is a possibility.  I am not sure what this site has to offer people (besides auto help) but my real expertise is in other areas.  I am a mechanical engineer with a wide background.  As far as this car is concerned I have a comprehensive understanding of how the computer works and what it is looking for.  However the manual that I have is not very helpful, and as you know it is difficult to figure out if the computer is getting the correct information (i.e. sensors working correctly, mechanical issue) or if there is some error with the sensors.  I do not have access to an OBDII except for the auto parts store.

Anyway, back to this issue for now.  I have read that after the throttle body position sensor is replaced the computer needs re-tuned at the dealership.  Is this correct?  Can you elaborate?  If so will it be drivable, say 7 or 8 miles?  Also, this does not make sense to me if it is indeed correct.  Perhaps the computer cannot adjust its own sensor input range/threshold/span and that is what the dealer does electronically.

Thanks again,

Darren


ANSWER: Hi Darren,
Thanks for for thoughtful response. The sensors often have expected characteristics that can be verified with a v-o-m. A shop-level diagnostic tool also will give operating paramenters which can be compared to expectated values.
On the question of post-repair tests, in none of the Chrysler manuals for the engine computer is there any suggestion that re-training or other parameter adjustments are required or recommended.
The automatic transmission however does have some for the torque converter, internal clutches, and pressure settings by interfacing with the diagnostic device only the a shop would have, following rebuild/part replacement but that too can be by-passed if you are willing to wait for the trans computer to re-learn with further driving.
So by my reading there is no reason to be concerned that replacing anything on the engine to require a visit to a dealership. The main issue with the TPS would be an open spot in the resistance reading as you carefully opened/closed the valve or voltage readings closed or WOT that were outside the limits I listed. If the computer itself is replaced, then a number of inputs have to be reset at a shop (VIN, theft prevention codes, characteristics of other accessories, for example).
I hope you find the cause of the remaining issue.
Roland


---------- FOLLOW-UP ----------

QUESTION: Hey Roland.

I ended up getting between .9 and 3.9 volts at the TPS so I replaced it.  I also replaced the TB gasket. The throttle seems more responsive now.  However, I still have the "missing" problem.  Other than search for a vacuum leak (which I have done numerous times) I'm not shure where to go now.  

I guess there is one possibility, that I don't quite understand.  I did take off the distributer to change the o-ring.  When I was putting the distributer back in I noticed that one of the bolt holes was a through hole (round) and the other was elongated.  So, I suppose there is a possibility that the distributer did not get clocked correctly.  However, in thinking about this, the distributer goes in a round hole and I have a "pin" on the outside of that so there should be no clocking from what I comprehend (other than orientation).  I don't see that I could have put it in incorrectly (not clocked to the EXACT position that I took it out in.)  I should note the distributer is oriented correctly and the roter is pointing at #1 at #1 TDC.

Any other ideas?  I'm getting desperate.  Thanks.

Answer
Hi Darren,
So long as the rotor points to the the #1 wire as you described the position of the body is not that crucial from what I read.
Maybe at this point taking a look at the cam/crank timing marks and doing a compression test would be in order. Also, I assume that the spark plug caps are integral with the wires, but in case they were seperately replaceable (as was the case with the Bosch system in earlier years) and you only have done the wire replacement you might want to replace the plug caps. Have you tried to pull the spark plug caps off the plugs, one at a time, to see whether one is less noticed when pulled which might focus your attention on a given cylinder as being weak. And how about another fault code readout?
Thanks for the up-date. I await news of the solution!
Roland