Very Strange Problem
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Very Strange Problem
My 1990 Aerostar has had the following problem off and on for a year and neither myself nor several mechanics have figured it out. The Starter, Battery, Air Filter, PVC and alternator have all been changed.
Whenever I put on the AC, or combo lights and ws wipers, or any significantly heavy load on the electrical, when I am going down the road everything is fine. When I slow down to a stop the volts will drop from around 14 to 11 then 10.5 then 10 then 8.5 and sometimes all the way down and then jump back up then start the whole cycle again. Sometimes the car stalls. Turn of the extra stuff and it idles perfectly.
When in park idle, everything runs fine. Put in neutral everything is fine. Car has been put on all the testers and nothing reports bad. Have reset the computer several times but no change.
Any thoughts would be greatly appreciatted.
John
Whenever I put on the AC, or combo lights and ws wipers, or any significantly heavy load on the electrical, when I am going down the road everything is fine. When I slow down to a stop the volts will drop from around 14 to 11 then 10.5 then 10 then 8.5 and sometimes all the way down and then jump back up then start the whole cycle again. Sometimes the car stalls. Turn of the extra stuff and it idles perfectly.
When in park idle, everything runs fine. Put in neutral everything is fine. Car has been put on all the testers and nothing reports bad. Have reset the computer several times but no change.
Any thoughts would be greatly appreciatted.
John
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From: PNW
Very Strange Problem
Maybe this is obvious and you've already looked at it, but I would check the idle speed. Sounds like it could be a little low since you don't have any problems in park or neutral.
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Very Strange Problem
I think Mikeman was referring to the idle speed control valve (aka idle air control). This is an electronically controlled valve on the side of the throttle body that kicks up the idle when the engine is under a load.
This valve often gets dirty and sticks. It is easily removed and can be cleaned by spraying with carb cleaner. The intermittent working/non-working status points to either a very dirty valve, poor electrical connection to the valve's solenoid, or just a plain bad valve that needs replaced.
Lots of posts about this problem on this forum if you need more particulars.
This valve often gets dirty and sticks. It is easily removed and can be cleaned by spraying with carb cleaner. The intermittent working/non-working status points to either a very dirty valve, poor electrical connection to the valve's solenoid, or just a plain bad valve that needs replaced.
Lots of posts about this problem on this forum if you need more particulars.
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From: PNW
Very Strange Problem
Take off the ice shield and look underneath the throttle body. It's on the throttle lever opposite where the cable attaches. The screw is small with maybe a 5 or 6 mm hex head. I'm not sure I did a good job explaining the location, but look around and you should see it. If you use it to set the idle, I'm guessing you would set the idle with the IAC disconnected (to eliminate any effect it may have) and the tranny in park with no load on the engine (AC off, no electrical loads such as fans, headlights, etc.). I don't have the manual that explains the proper procedure, maybe someone else on the board has done it.
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Very Strange Problem
I have looked all over for this valve. I have the manual and all it mentions is the Throttle Position Sensor. This is a 4.0L Fuel Injected Engine (I forgot to mention this). There is no reference to the valve.
Any other thoughts?
Thanks,
John
Any other thoughts?
Thanks,
John
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Very Strange Problem
Hood up, facing engine, follow the black rubber air snorkel to where it attaches to the throttle body. On the right side of the throttle body, you can see the base of the IAC valve, silver and about the size of a 50 cent piece. The cylindrical valve extends toward the rear of the engine and is held on by two bolts and has a two wire connector attached. Remove the electrical connector and the two mounting bolts and that's all there is to taking it off. Clean the area that extends into the throttle body with carb cleaner, several times. Threre is a small pin that meters the air flow and any gunk will cause the pin to jam. Replace and test.
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Very Strange Problem
For every car that I own, I add more ground wires. I use 4G neg battery cables with loops on each end. Cost about $5 from your local parts store.
Usually, I run one wire from the alternator to the firewall to help the computer's ground, then I run another from the block to the negative battery terminal. The voltage gain at idle is why I do this, which can help the IACs performance. I always brush the paint off the metal with a wire wheel, then add dielectric grease (or vasoline) after I make my connections.
You can check the ground of your car (Running) by measuring the mV from the alternator case to the negative battery terminal. In theory, you are trying to have 0mV, which is impossible in the real world. Most cars range from 100mV to 250mV-- 300mV plus means your grounds are going. Loose screws & wire terminals, along with frayed straps are usually the cause. On most of the cars that I added the extra ground wires, the reading was around 15mV.
Usually, I run one wire from the alternator to the firewall to help the computer's ground, then I run another from the block to the negative battery terminal. The voltage gain at idle is why I do this, which can help the IACs performance. I always brush the paint off the metal with a wire wheel, then add dielectric grease (or vasoline) after I make my connections.
You can check the ground of your car (Running) by measuring the mV from the alternator case to the negative battery terminal. In theory, you are trying to have 0mV, which is impossible in the real world. Most cars range from 100mV to 250mV-- 300mV plus means your grounds are going. Loose screws & wire terminals, along with frayed straps are usually the cause. On most of the cars that I added the extra ground wires, the reading was around 15mV.
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Very Strange Problem
I had the same problem on my 93 4.0L and my problem was so simple that it was overlooked by the mechanics, but a friend found it! It was the main power lead from the battery to the starter solinoid, it was badly corroded and we just had to touch it and it broke off completely. I put a new connector on the end at the solinoid and that solved the problem for me. I hope that yours is just as simple.
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Very Strange Problem
Maybe some good news. First I cleaned the IAV and MAV. No real effect. Then per recommendation I added an extra ground from the altenator to the firewall and the battery to the block. No major change. I then change the PVC valve and cleaned all the electrical connections. Again no change.
Last I did 2 things. 1st, I changed the starter solinoid, I noticed some rust on the connectors. Next, about 2 years ago, during a Jiffy Lub visit, they lost one of the screws holding down the air cleaner cover. Over the next year, the back holder on the other screw came off and the screw has just been barely holding the cover on. I changed the air filer, cleaned out the air filter area and took 2 plastic pull straps and tightly closed the air filter cover down.
Since this last 2 changes, the car has been running very well and seems to hold idle nicely. While it is too soon to say for shure, I think the problem may have been resolved.
Thanks everyone for your input. This is a remarkable web site and the knowledge here is very impressive.
John
Last I did 2 things. 1st, I changed the starter solinoid, I noticed some rust on the connectors. Next, about 2 years ago, during a Jiffy Lub visit, they lost one of the screws holding down the air cleaner cover. Over the next year, the back holder on the other screw came off and the screw has just been barely holding the cover on. I changed the air filer, cleaned out the air filter area and took 2 plastic pull straps and tightly closed the air filter cover down.
Since this last 2 changes, the car has been running very well and seems to hold idle nicely. While it is too soon to say for shure, I think the problem may have been resolved.
Thanks everyone for your input. This is a remarkable web site and the knowledge here is very impressive.
John
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