96 Caravan 3.0 Throttle Position Stutter/Miss

I have a long term engine stutter or miss at a certain throttle position, just above cruise speed. It's been going on for 30k miles with no change. Engine computer reports #3 cylinder misfire. Otherwise it runs smooth and gets good fuel economy.

Spark plugs, wires, rotor and cap have all been replaced. Doesn't seem like it should be the injector, since it performs well in all other throttle positions and the miss is erratic when it occurs, sometimes worse. Can the throttle position sensor cause this type of malfunction? Or? Carbon in air horn? Just wondering if anyone else has had this type of malfunction and resolved it....

The TPS should throw a code, but it's possible that it won't. If it stutters at the exact same pedal position (most 3.0's don't have a tach...) then it's likely that the TPS has a dead spot. Replace it.

However, cleaning the injectors, Air Horn and Plenum is probably a good idea, and may solve the trouble.

Last, I have a 3.0 that would hesitate now and then, then it finally got worse. One day it stalled out, but would restart, but not run enough to move. Suprisingly, it was the fuel pump that caused the issue. There's a thread here on AF I started that explains it in more detail... http://www.automotiveforums.com/vbulletin/showthread.php?t=529639

Tom

Did you check the CPS and MAP sensor ?

I have cleaned the air horn and run cleaner through the injectors, but I haven't taken the plenum apart as that is a little more involved. I've wondered about the TPS -- as the problem is definitely throttle position related. Engine load doesn't affect the stuttering symptom. I have discovered that it is not only the #3 cylinder, but jumps around. If it is possible for the TPS to have a narrow dead space about midway between idle and full throttle that would explain the problem. I pulled it out the other day to inspect it and of course there is nothing to see, and I don't know how to test it for performance, or if there is a multimeter test proceedure. Perhaps I will simply have to go through the process of elimination by replacing the components most likely to be causing the problem in order of priority. However that can be expensive if the culprit happens to be the last thing on the list -- it's always good to narrow things down with good diagnostics.

Thanks everyone for your help. I'll post as I go on this one.

Mark

I bit the bullet and replaced the throttle position switch a couple of days ago, which didn't alter any symptoms at all -- hmmm.

I have a 95 Caravan 3.3l which began to stutter and hesitate on light throttle applications. No codes but I found that a cracked vacuum line was the cause. The hose was attached to the EGR. If you have a vacuum gauge connect it to the intake and start the engine. Pinch or plug as many vacuum lines as you can one at a time until you see an increase in vacuum pressure. My engine would wistle every time I lightly touched the throttle. Then go away under acceleration. Changing gears from drive to reverse would cause the engine to hesitate. The vacuum leak was causing a lean condition in the engine.

Rich

A vacuum hose leak might be the problem. The symptoms are getting worse lately, enough so that I have discovered the missing is caused by excess raw fuel. When stopped in drive, accelerating with the brake on, standing at the tail pipe one can see raw fuel spraying out. Basically it is flooding. It is now possible to kill the engine unless the throttle is depressed all the way, opening the intake enough to allow more complete fuel combustion. At this point fuel consumption has increased significantly.

Check for a vacuum leak which would cause the fuel pressure to increase. Zero vacuum allows full fuel pressure to the injectors. I would pull the vacuum line off the fuel pressure reg and verify you have at lease 15in of vacuum at idle. I have had to replace most of the OEM plastic vacuum lines already. They get brittle and crack causing the drop in vacuum.

Rich

A vacuum hose leak might be the problem. The symptoms are getting worse lately, enough so that I have discovered the missing is caused by excess raw fuel. When stopped in drive, accelerating with the brake on, standing at the tail pipe one can see raw fuel spraying out. Basically it is flooding. It is now possible to kill the engine unless the throttle is depressed all the way, opening the intake enough to allow more complete fuel combustion. At this point fuel consumption has increased significantly.

if all the wires and plugs have been changed and the missing jumps around to other cylinders as well I would check the ignition coil, or just replace it , I think yours is pretty cheap. There is no code for a faulty coil, it either shows up as missing or if there is a problem with the coil voltage primary voltage.

are you getting any code for "no distributor refrence signal- pickup coil or cam sensor under the rotor"?

are you getting any code for "no distributor refrence signal- pickup coil or cam sensor under the rotor"?
My son thought of that too... just haven't had time yet to try replacing the electronic module in the distributor. But I'm also wondering if it would spray such a rich mix of fuel out the tail pipe if it were an ignition problem. It's fine at idle and mild acceleration -- medium acceleration it seems to be choking out on excess raw fuel that sprays unburned out the tail pipe -- hard acceleration it opens up and burns rubber.

Now that the problem is getting worse I think I'll borrow the computer again and see if I get more code than I did at first.

You all have given me more ideas than I expected. After what I've tried thus far it seems to come down to two basic things; a vacuum problem or distributor module malfunction. I think I'll go for the vacuum testing first.

Interestingly, the local Chrysler dealer tech didn't promise any quick diagnosis. I could see that if I gave it to them I might be walking out with an over-fixed vehicle just the same as I would have to do by trial and error. It might take me longer -- hopefully it won't cost me more!

some people have reported that if the fuel regulator is faulty that it may be leaking fuel and the vacum hose attatched to it will be sucking fuel down into the intake manifold. While it is running , pull the vacum line off the regulator and see if there is any gas there. There shouldn't be anything.