My mom had a 93 Sundance she has had from new. It was one of those years that the paint fell off of so it looks like crap. She lived in southern Colorado(desert) so the body is still real good minus the paint missing. It was acting up and she dident want to put any money in it so she was gona take it to the junk yard and get rid of it. I convinsed her to give it to me instead and if I couldent get to the bottome of it I would take it to the junk yard. The car only has 120,000 on it so its low miles for the year so I hate to give up on it but iam getting sick of this thing. It is a 4 cyl with a 5 speed and for what ever reason it will just start bucking and jerking at all throtle positions except idle and WOT. It isent just a little hickuping either. It will go from what ever throtle position you have it at to idle and back in a split second and keep doing this over and over indefinatly. It dont matter wheather you are cruising down the highway at 60 or just starting off from a stop. While taking off from a stop it gets real bad and makes me look like I have never driven a 5 speed in my life. The car starts bucking and jerking wildly. You have to either flore it or let off to idle to get it to come out of it. I have been trying to drive it for almost a year now and most of last summer it just sat cause i dedent want to mess with it. I was told to replace the throtle posion sensor and that seemed to fix it for a month or two then it started doing it again. Then it got cold last fall and it ran PERFECTLY all winter. I left the truck sit all winter and drove the car with no isues what so ever. This spring as soon as it started warming up the probelm came back intermitently. A budie found a cracked vacume line and replaced it and it ran fine for anouther month. Now the problem is back. It will run perfectly fine for a long time then all of a suden while cruising down the road it will just start bucking like mad with no warning. I would love to throw the car in the garbage but with fuel prices I need it for a DD to save some money. The dumb thing will pull well over 30 MPG so there is a HUGE financal reason for keeping it alive vs driving the truck. I am looking for ideas on what to do next. I know it needs a tun up but I dont wana put money in it till I get it to run rite. If I thought the plugs and wires could cause this I would replace them but this seems more like a sensore isue to me. The budie told me today that he has heard of the computer needing to be cleaned. He said the computer or something was located in the intake tube and acted like a mass air flow sensor and he had heard of them getting dirty and causing isues before. Any Chrysler gas gurus out there???

 

So I may be on glue but it sounds a bit like a prob I solved on my mother's Plymouth Horizon years ago. An old codger on allpar.com taught me a really cool trick to find vacuum leaks on gassers that cause really rough and weird engine conditions. Start the engine and do whatever you need to do to make it run rough while it is is park. While outside on a calm day or in a well vented garage, grab a handheld propane torch. Turn on the propane but do NOT light the torch. Slowly play the propane stream over the many vacuum lines of the car. If at some point the rough condition goes away, you have a vacuum leak and it is where you were pointing the the stream of propane gas when the rough condition went away.

 

Check the fuel filter. Maybe some rust is breaking out of the tank and plugging it up intermittently.

 

They do draw air through the computer but I thought that was to keep the computer cool when it gets really hot in the engine bay. I may be wrong but I do remember reading that somewhere.

 

My first thought was also the fuel filter or a vacuum leak. Another way to check for vacuum leaks is to spray carb cleaner on the hoses and see if the RPM raises. Or you can cover the throttle body (or air intake) and see if it dies.

 

First thing I would do is check the computer for any codes. Just because the CEL light isn't on doesn't mena there aren't any codes stored. The CEL bulb might even be burned out.

Mopar has a really easy way to check the codes. Don't start the car or even bump the starter. turn the ignition on, off, on, off, then on and leave it on the third time. If your CEL bulb isn't burned out, it will start to flash. Nearly every time it will flassh once, then twice. That is code 12. All that means is the battery has been disconnected in the last 50 or so key starts. When it flashes code 55, it means the end of the test cycle. Anything else will tell you where to look.

Personally, I'd clean the throttle plate in the throttle body. When these get dirty, they can cause all sorts of problems.

 

And don't overlook the engine to chassis and chassis to battery terminal ground terminals and cables.

 

Thanks guys. I had been contemplating the propane idea. I have done that before but i couldent remember if we used propane or what it was. I also suspected that the computer was in the intake tube most likely to keep it cool rather than build a flow sensor into it. It dont make sence to me to use the computer as a sensor when you could make the sensor a seperate item but engineres dont always do stuff that makes sence.

I did put a new fuel filter on it and it seemed to fix it for a few weeks back when mom was still driving it but it dident last long. Honestly no matter what I do to it it runs good for a month or so then rite back to the hickups. I have put on a few new vacume lines and both times it ran fine just long enough to make me think maybee that was the problem then it started acting up again. The only thing that has seemed to make a long term diference was the winter temps. So long as it stayed below 25deg it ran like new. I will give the propane a whirle and see if i can find any more vacume leaks.

 

Well the propane did nothing. I had the valve all the way open and found nothing. I even tried putting it rite in the intake bypassing the air filter and it did not raise the RPMs at all. I did find one major vacume leak but it still dont run any better. I may try a tuneup next but I dont see how plugs and wires could cause it to run this way. I would think it would run bad all the time if they where bad enough to be the isue.

 

Choke issue ????


Cheers,
PISTOL

 

It might be worth throwing a pickup plate in the distributor. They were a common problem for stalling and such, and are not expensive. Check its connection first, and while it's out, make sure the tone-wheel under it hasn't come loose.

 

A 93 would be fuel injected.

That does remind me of a problem that was fairly common on those engines. Check out the temp sensor circuit, they tend to have problems with the connection at the sensor. This will cause all kinds of weirdness.

If you have access to a scan tool , the easy way will be to simply read the temperature after sitting over night & watch as the engine warms up. You can also check the rest of the sensors the same way.

BTW. . . . check your O2 sensor. A bad O2 could cause a problem like this.

 

Thanks for the input. I will look into the temp sensor wiring and see if I can find someone with a scaner to see what it is reading. I have been thinking of plugs and wires and most likely a new cap and rotor while I am at it. I honestly wouldent be a bit suprised if its all factory original yet. My moms ex was not good at doing maintenece to anything. I have just been reluctant to spend much money on it till I figure out what is actualy wrong.

 

How about the coil pack. Had one that was running great in the winter and bad in the warmer weather. Changed the coil and it ran great through all seasons. Of course that is when a car was a car.

 

Call around to some auto parts stores in your area. Chances are one of them has a reader you can use. I know for a fact that Oreiley's will let you use theirs, my napa here in town does not, and neither does the car quest, so it may be a crap shoot. Most times you just have to leave your license as collateral.

I would definitely start with codes though, sounds as though anything else is really just a guess at this point. It could also identify a problem through multiple sensors that can not be remedied with changing out just one. If you had a major vacuum leak and it did not change things, my guess is you may have a dynamic problem, not just one part. Might take multiple scans and multiple headaches...