Hello all,

I'm having an issue with my van idle and I was hoping someone here may be able to help out.

Background:
I bought a 1995 Dodge B3500 camper conversion van (Sportmobile) last summer with 200K miles. When I bought the van last year I noticed the engine would stall sometimes at idle with the A/C turned on. I didn't drive it much as I had to do a lot of work on it (new fuel pump, new Bilstein shocks, Hughes aluminum plenum plate, fan clutch and mostly all of the camping systems, water, electric, generator, etc).

So this summer I've been actually driving the van and even with all the work I've done the stall issue at idle still occurs occasionally with the A/C on.

Stall Conditions:
-Engine is at operating temperature in closed loop
-Car is driving, usually in town with regular stop lights
-Weather outside is usually warm/hot and fan clutch is partially/fully engaged depending on how hot it is
-A/C is on either normal or max
-Stall usually occurs during a deceleration event, for example when I'm stopping at a light
-Engine starts right up after stall, and runs normally with no other signs or issues

Here is what I have done so far (as general maintenance and to address this issue):
- New spark plugs, wires, cap and rotor
- New O2 sensor as it was suggested I replace it due to the oil the old plenum was leaking
-Checked back pressure on exhaust system and it's about .5 PSI so catalytic converters are flowing
-Checked fuel pressure at rail and it's about 35 PSI at idle and with engine running
-New PCV valve (Mopar part)
-New Camshaft Position Sensor (Delphi)
-Cleaned the throttle body thoroughly including the IAC port and small pinhole airports
-Cleaned MAP sensor ports in throttle body
-Cleaned IAC port in throttle body
-Replaced IAC with Standard brand part - made no difference when using older IAC
-Reset PCM by leaving battery cable unplugged for 30 minutes and also holding key in run position
-Tested EGR valve for vacuum and diaphragm integrity
-Checked for vacuum leaks by plugging off hoses on intake manifold

Testing Conditions:
In my driveway I start the van. When the engine starts it idles smoothly in open loop, and in closed loop, no other issues. If I then after the engine is warmed up, I turn on the A/C I can feel there is no adjustment to the idle. The engine continues to run at the same RPM's as when the A/C is off. Based on what I understand the PCM is supposed to command the IAC to increase idle by about 100 RPM's to compensate for the additional load of the A/C compressor. I don't believe this is happening. The A/C system is running fine, blowing cold air. If I then put the van in gear with the A/C on I can feel the RPMs are just too low.

My Hypothesis:
I believe what is happening is that the engine is simply stalling out due to the load of being in gear, the fan clutch engaged, and A/C compressor engaged. I don't believe the PCM is receiving the signal from the A/C system to command the IAC to increase idle.

My Current Troubleshooting Steps:
In reading the service manual it says "When the A/C switch is in the ON position and the A/C switch is closed, an input signal is sent to the PCM. The signal informs the PCM that the A/C has been selected. The PCM then adjusts the idle speed through a pre-programmed RPM through the idle air control (IAC) motor to compensate for the increase in engine load."

To test this, I have disconnected both the high pressure and low pressure A/C switches. With the engine off I used a multimeter to check that both switches are closed, which they are (assumed this since the A/C works). I also used a multimeter to test the plugs that connect to the pressure switches. Here is where I am struggling to understand.

Turn Key to On Position (AC turned off)
Low Pressure Switch - I get 11.3V on one terminal of the plug and about 10mV to the other terminal of the plug (C102)
High Pressure Switch - I get 11.3V to both terminals of the plug (C103)

Turn Key to On Position (AC turned on)
Same results as above

I'm not sure what this is telling me or how to troubleshoot this. Does anyone have experience with troubleshooting this issue or can give me some advice on what to test next? I'm just not sure what the signal is that the A/C control is sending to the PCM. Is this the 11.3 volt signal that I am seeing on the multimeter? Based on the diagram in the service manual, it appears the brown wire of the high pressure switch connects to the PCM on port 27 of the PCM. I'll include a picture of the wiring diagram.

 

Remove the engine cover, the air filter cover, and then air filter. Start the engine and repeatedly place your finger over and remove from the hole at the rear of the throttle body where the air gets drawn into the IAC valve. This will force the IAC to open and close as it tries to maintain idle. Often, doing this will kickstart the IAC into working correctly. In some circles this is referred to as, "the finger trick." FYI, the IAC only operates when the throttle is closed, as in your foot is off the gas pedal, so revving the engine will not help.

 

Okay, thank you for the suggestion! I tried this test. When the engine was cold, and not yet in closed loop, I placed my thumb over the IAC air port and I could feel the IAC pulsing and retracting, then when I let my thumb off the air port I could hear the engine RPM increase high and come right back down. The second test I did was to let the engine warm up and idle and view the IAC from above while I turned the A/C to the ON position. Looking down at the IAC with the air cover off I can see the IAC move inward when the A/C is turned on. When I turned the A/C to the off position I could see the IAC move to close off the air port. So the RPMs do increase slightly now with the A/C on so possibly exercising the IAC helped it out. Based on this test it does give me confidence the IAC is functioning as it should in idle and with the A/C turned ON.

Interestingly when I was testing in my driveway the van engine died while idling and the AC was turned OFF. No warning, or sputter, the engine just died at idle. It started right up easily. It was hot outside about 95 degrees and the car had been idling for about 30 minutes. It may just be something related to the engine getting warm at idle and not related to the A/C being on at all, maybe just a coincidence. I'm leaning toward replacing the distributor pick-up sensor (camshaft position sensor). I know the previous owner replaced it right before I bought the van but I'm not sure what brand of part he used. I had a 93 Mustang back in the day that would just cut out on a hot day and it was the pickup sensor that would fail intermittently. Once I replaced it the car ran perfectly.

I got a pickup sensor coming today to try out but any other advice on what I should try? This issue only appears to happen when the van is idling on a hot day and the engine is warmed up to the point where the temperature gauge is at the half halfway mark and the fan clutch is engaged.

 

The engine will run with the cam position sensor unplugged, but it will not start. I got that from someone here. So it should not be the cam position sensor.

 

I had that issue once, turned out to be the crank sensor. On top of that, I went through 3 crank sensors before I found one that wouldn't turn on the CEL every so often with a random misfire code.

 

Thanks all for the suggestions! So here is the latest update. I installed the new distributor pick-up sensor (camshaft position sensor), it's a Standard brand part, and it *seems* the issue has been resolved. I drove the car around town today in 105-degree weather with the A/C on and no stalls at idle. I'm going to drive it for a few more days to confirm the issue is fixed.

One thing to note, the acceleration is much stronger and smoother now with the new pickup sensor. The engine timing also seems much better than before. This leads me to believe there were at least some issues with the old sensor. Possibly the old pickup sensor wasn't sending good consistent timing data to the PCM and this would cause the low idle stall. It's my working theory for now, but more driving is needed to confirm it's fixed.

 

Interesting write up.

 

The sensor in the distributor is used at startup, and then ignored...... At least, that is my understanding of it.... You should be able to disconnect that one, with the engine running, and the engine should continue to run.