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Discussion Starter #1
Sorry to raise an old and tender subject with many. But I need clarification regarding a possible solution found elsewhere on Allpar.

This involves the dreaded random stalling on Caravans, Voyagers, etc. Mine is 1988 model with 3.0L. My set of symptoms are similar as reported by others - random stalling only once in awhile, restarts immediately (or if at highway speed may restart itself while still moving), not related to cold starts or stalls when approaching a stop. And NO codes are set. I only read a 55 when I check; the "last message" marker. Happens at highway speed and also when toodling along at 25 mph. I do note, however, that it seems to happen when I "coast", taking my foot off the accelerator for a moment. This makes the following seem significant.

I note the interesting description by Ron Wirth at this page (scroll down somewhat)..... http://www.allpar.com/mopar/3.html ...... wherein he relates that a sharp mechanic knew about this problem and discovered that it had to do, at least in some cases, with a sticking "fast idle servo" in the throttle body. It seems that the clearance in there is very tight in the cone valve area. Small deposits build up in there, smog particles or dust perhaps, facilitated by changes in humidity and temperature, which can cause a subtle and random sticking.

I've read quite a number of posts about the MAP sensor and crank sensor, and those are on my list. Also the ASD relay. I've already verified fuel pressure and because of a previously bad fuel pump years ago that could not maintain pressure under demand, I've replaced my pump again, even though the former one is probably OK (will keep for spare).

First though, I'm game to try cleaning that item that Ron mentions, but I need some clarification. I cannot find a manual reference to a "fast idle servo". I think this means the AIS motor or something else related to idle control, but Ron mentions that one should be careful to not get solvent on the motor itself, and not to just spray solvent into the intake which can cause problems with the idle speed controller. Just clean the "fast idle servo" in the throttle body. Do I interpret this correctly to mean removal of the AIS motor (two bolts and watch that the O-ring doesn't come off!), clean the orifice in the throttle body and then reassemble? If not, can someone clarify the idle speed controller parts/function/location on or near the throttle body? Or if someone knows how to contact Ron Wirth could you get him to clarify? Thanks to all.
 

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I would have to say that the 'fast idle servo' is the AIS motor. The 'cone valve' he speaks of confirms it.
Remove and clean the cone (pintle) and it's bore or replace the AIS. Clean the throttle bore and blade as well. These could carbon-up and restrict airflow or stick.
If the motor is starving for air on decel (coast), it can cause a stall.
 
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Thanks, Imperial. I have been confused by the difference between the terms idle air controller, idle air actuator, idle air control valve, and AIS motor. For clarity, is the AIS motor the same thing as the "actuator" that controls the valve, which is essentially the pintle that moves into the cone orifice? I've seen references on parts websites that the AIS motor can be replaced separately from the idle air assembly, so I assume that the assembly includes the control valve?

I removed the air breather pipe between the air cleaner and throttle body intake and looked into the intake... it's definitely dirty in there. I want to pull the TB entirely to clean it properly and also to more easily inspect and clean the idle air orifice. It appears that I only need to disconnect the idle air connector, the TPS connector, two vacuum hoses at the top, and the throttle and kickdown linkages, plus remove the kickdown linkage support bracket, before I can pull the TB. All sound correct?
 

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AIS (Automatic Idle Speed) motor is all I've ever heard Chrysler call it. Many manufacturers have there own name for it. They all basically serve the same purpose, to add air to the intake manifold to control idle speed.
I don't think that the Chrysler AIS is serviceable other than cleaning.
With it out of the throttle body and plugged into it's connector, you can have someone roll the ignition key on to watch it's movement.
Removing the t/body for cleaning is the best way. You might want to have a new base gasket for it if the original isn't re-usable.
 
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Discussion Starter #5
OK, thanks again for the clarification. Looks like I'll be spending my Saturday afternoon productively.
 

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A bad battery will also cause some weird things, seems like the computer forgets it
idle settings and has to relearn- creating numerous stalls until it settles.
 
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Discussion Starter #7
Thanks also to AC TC for the battery advice, but I'm pretty sure that's ruled out. Battery fairly new, connections tight, terminals are corrosion protected.

Revising problem description:

Throttle body has been cleaned, including idle control area. Problem still occurring. Contrary to my original statement that it happens at both slow and fast speeds, it seems to only happen during highway travel. The slow speed report was only one instance, and that happened when I had just come off the highway and had slowed to about 25mph after turning off the exit ramp,. I can see where idle speed problem would be in effect when coasting down from highway speed on that exit ramp, but under power on the highway, it would seem to rule out idle, or fast idle, control being a problem in the throttle body.

Any thoughts on causes for stalling at highway speeds? Still very random, and once I pull over I can restart within a couple of minutes and then keep driving. Last night when it happened, it stalled again right after restarting, but after another minute, it started fine and I was able to continue driving home.

As before, there are no codes in the SMEC after occurrence(s) other then end-of-file 55.
 

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Possibly loss of either spark and/or fuel?
Having a helper along to crank it over while you check for spark could help.
I don't know if you have a capped test port on the fuel rail that you can push the port schraeder valve in on and get a 'spritz' of fuel into a rag? This will indicate fuel pressure was present up until the point of stall.
The distributor may be acting up when warm? There is a tutorial on distributor service for the MMC 3.0L on this site.
A good scan tool may show what was 'lost' on a road test during stall on the sensor display screen.
 
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Discussion Starter #9
Thanks, Imperial. Can you point me where to find that distributor tutorial? I am unfamiliar with this forum site. I'm still thinking something mechanical, like a fuel or sensor problem, as it seems that anything ignition related would set a code. But I'm willing to check anything at this point, including distributor, Hall effect pickup, etc. The problem actually got worse after I carefully cleaned the throttle body, which tells me that I was more or less in the right place. It could even be something in the wiring harness nearby.
 

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If yours is the 'optical' photo-diode distributor, go under the 'Tech/Fix/Engines' tab at the top of this page. From there go under 'Allpar repairs'. The distributor link is further down the page. I know that the 3.0L distributor went to Hall-effect later.
If the PCM sees the sensor or 'whatever it is turning off' still within 'spec' or operating parameters, it may not throw a code. Codes are nice, but not always there. That's when diagnosis has to be done while the culprit is acting up.
Many electrical problems can be intermittant and the wiring harness needs to be checked out. Does it seem temperature related in any way? Has the stall occured within the first 5 minutes?
 

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Stalling at highway speed and recovery after sitting could also be connected to the Catalytic Converter. As you're tooling down the road, if the converter is plugged, the exhaust back-pressure can build up. Since the engine is an air pump, and can't exhaust through the plugging converter the engine stops. When you sit at the side of the road, the pressure bleeds off through the converter. Now you can go on your way till it happens again. A couple of ways to diagnose the problem is:
  • Have the exhaust back-pressure checked at a mom and pop muffler shop. The test is usually free.
  • Lift the hood at night and see if the exhaust manifolds are glowing dull to bright red. That's the heat being trapped. It's harder to see during the day.
  • Do the same for the Catalytic Converter, if it's plugged it's going to get really - really - hot and may even start glowing.
One rule of thumb I've followed is:
  • If the engine dies like you turned off the ignition, the problem is electrical.
  • If the engine sputters and dies like it's struggling to continue, it's fuel related.
so, how is it dying, like you turned off the ignition or sputtering and coughing as you try to keep it going?

This problem may have to get worse before you can find the problem.
 
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Discussion Starter #12
Thanks again for the replies/tips. In answer to LEVE's question:

>>so, how is it dying, like you turned off the ignition or sputtering and coughing as you try to keep it going?

It happens within a few minutes of driving at highway speed. It's a sputter or stumble first. Not an instant shutdown like one would expect with an electrical problem, although I know that's a generalization because electrical could include a wiring issue that causes an intermittent with one of the sensors, etc. When going down the highway, there will first be a noticeable kick or stumble for a second or two, but no stall, then another stumble or two a few seconds later and then it stalls. It initially felt so much like a fuel pump problem (that I had experienced in the past), that I had the fuel pump replaced ($375 part and labor) only to discover that, this time, it wasn't the problem. I now have a good spare pump(!).

Will definitely do a visual check for overly hot exhaust manifold and catalytic converter at night, especially right after a "stumble test" while I'm on the side of the highway. Never thought about plugged exhaust and back pressure buildup. Will also check for a "fuel spritz" at the schrader valve right after an event, as Imperial suggested, to make sure that I still have fuel pressure right after an event. I don't think it's a spark or ignition issue because I can drive at slower speeds all day long with no occurrences.

Another thought on potential fuel starvation: If the problem is with the fuel pressure regulator, usable pressure from the pump may actually be reduced just enough in the fuel rail that at highway speed, with increased injector draw at wider pulse widths, fuel demand overwhelms available pressure. In which case, the injectors would fail, within minutes at highway speed, to properly atomize fuel and the engine would stumble and kick as though I'm running out of gas, which is how it feels. This would also explain why the engine restarts almost immediately after a stall - the fuel rail is repressurized and driving at slower speed doesn't cause the fuel demand to be high enough to overwhelm the reduced available fuel pressure. Does this seem plausible? Or would the basic fuel pressure check, if within tolerance, rule this out?
 

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Or would the basic fuel pressure check, if within tolerance, rule this out?
I doubt that a fuel pressure check would help a whole lot. You've already replaced the fuel pump, so pressure should be good. Most tests are taken at idle, and not while you're running down the street with the engine under load... hence the problem won't show up.
 
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Thanks, LEVE. So does the fuel starvation scenario I mention seem like a possibility? Should I consider just replacing the fuel pressure regulator to rule that out, since I can't really get a valid pressure check under loading conditions?
 

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I wouldn't replace anything just yet. If you do have a fuel pressure test port on the rail (some didn't), you could attach a (borrowed or cheap) fuel pressure test gauge and have it under the w/shield wiper while you're driving to note the pressure. Just don't use the wipers. Watch for the pressure drop-off as it dies.
On a 22 year old van, I wouldn't be surprised at rust inside the fuel tank plugging up a fuel pump sock or filter. But as others have stated, this could be an electrical issue. Keep on going with the diagnosis.
You may be able to repeat the stall once it starts happening by 'power-braking' for short periods. This way the van would be stationary and allow you to go under the hood to observe things like distributor spark. Just don't stand in front of the van and don't power-brake for more than 10 seconds without a 30 second breather in neutral to cool the ATF.
 

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Mine was stalling when Cold - I had replaced broken Vaccuum Hose to IAC but Port was clogged - Ran perfectly Warm but Cold stalls - Uncloggd IAC Port at TB per above Post & bingo, no more Cold stalls ~! - Mine has slight vapory haze at Exhaust until warm - When it was stalling Cold it had no "Cold haze" at Exhaust when I had no IAC function - Great Thread BTW~!
 

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I just rebuilt my engine in mine 3.0 once I was lernded by some of the fine folks on here about how to properly drop the distributor I got it running. Anyways I had some codes to fish through and ordered all new aic, tps, o2, map sensor and egr transducer. As I pretty much had codes for all of them and the ones I did not figured what the heck replace them anyways why I was at it. When I had engine apart I cleaned all of the carbon out of EGR assembly and plenum and tested egr valve. But I had nice smooth idle at start up but once I started driving a little ways check engine light came on and my idle would drop at stops almost to point of dying. Transducer showed up today I installed reset codes and my near dying issue went away so did all my other codes. now I am down to one engine position sensor its amazing what egineers will do to punish you on performance when you are not meeting emission standards in the ECM. Do you have a code for improper exhaust gas measurement when egr opens?
 
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