My 1995 XJS with the 4.0 liter AJ16 engine keeps stalling when I shift from Park into Reverse, Reverse into Drive, and occasionally at stop lights. It has zero error codes in its OBDII system. Throttle body is clean. It seems like the RPMs drop too far when shifting. Could it be the air idle control stepper motor? Any other ideas?
Edit: Seems to happen mostly when cold, rarely after warming up.

 

Check your transmission fluid level. Low fluid can cause this.

 

Without question, the tranny fluid level would be the first thing to check.

What are your RPMs at in gear and in Park? Are the RPMs steady? What happens to the tachometer when you load up the engine with AC, head lights, etc. Watch the needle as you turn things on.

How old is your battery?

 

I'll check exact RPMs, but it's in the 600 range in Park, then drops (as expected) shifting into Reverse and from Neutral to Drive. Volts definitely drop when I turn on head lights or other electrics, haven't tried AC yet this year. Battery is only about a year old.

 

Mine was doing the same thing and it started quite some time after I purchased the car. It turns out the previous owner had set the idle using the accelerator cable. It eventually stretched and the idle dropped and car would sometimes stall out, but would immediately start back up. I reset my throttle valve (there is a set screw) and haven't had that problem since.

 

Your idle may be too low. That would cause this issue.

When warm, RPM should be at 700 in Park. 580RPM in gear. That's when warm.

If you're seeing that cold, then we need to address this issue. Before we start down this path, I'd like you to check that.

Thanks.

 

Thank you, Vee, Rick and Scott.
I checked the automatic transmission fluid cold yesterday and it was around the two lines well below the HOT region. I'll check it hot today. I'll also check the RPMs both cold and warm, both Park and Reverse / Drive. Idle air control valve looks pristine, but didn't check any further.

 

OK, doesn't sound like the transmission fluid will be the culprit then. That's certainly in the ballpark.

I would like to know about the RPMs. It's possible someone effed around with the butterfly plate on the throttle body trying to solve a problem that couldn't be solved that way. The gear shouldn't matter, park or reverse should carry the same RPM. But I do want to know that and in Park. Cold. and Hot.

Vacuum leak can also cause what you're experiencing. You would have to place some plastic at the MAF, to block it off, then unplug the hose at the engine camcover and blow smoke through that until you find a leak. I had a similar problem one time at the intake manifold gasket. It leaked just enough that I would see a dip in my idle RPMs every 32 seconds. When loaded with the AC, headlights, etc, it could stall me out sometimes.

 

Update - started the car, shifted through gears, let it warm up, shifted through gears again, and checked transmission fluid levels.
Cold: Park, 800 RPM; Reverse (did not stall), just under 700 RPM
Warm: Park, 700 RPM; Reverse stalled the first time, second time, just under 600 RPM

With the engine warm (not sure if the transmission was fully warm), the transmission fluid level was well below the "HOT" region. I added about 200 mL of transmission fluid.

Will report back with more testing later this week.

 

Update 2 - it took substantially longer than a week, but after adding a total of about 500 mL, it has not stalled again! Even with the AC on yesterday, it worked perfectly.

Thank you, Vee, Rick, and Scott!

 

Great, what transmission fluid did you use? I am using ZF 6 , it’s a ZF transmission I don’t know what is commonly used . AJ 16 auto.

 

Generic Dexron V from Advance Auto.