Surging/Stumbling/Jerking at cruise speed?

[PSITSI]

Ok, I tried to find something on this in the forum, but came up short. I have a 1990 Talon TSi AWD, with 70,000 miles, and it is BONE STOCK, not even an aftermarket BOV. My problem is that I am having some problems getting it started when cold. I get it to start, but it stumbles and dies a few times before I can get it to stay running. Then, when it does run, it idles erratically. The car accelerates and decelerates nice and smooth, but at steady throttle, say with the cruise set (at any speed), I can feel the car jerking/stumbling/surging. I have gotten a few suggestions, such as "maybe the transfer case is the wrong ratio" which doesn't make any sense to me for my problem. It has new plugs and wires. I am thinking maybe the fuel pump? I just think its weird how it accelerates beautifully, but at cruise its pretty crappy.
Sorry if this problem has been addressed before, but I couldn't find anyone with this similar problem. Any help would be greatly appreciated. Thanks!

 

[Eastwood95]

If I were you, I would start by doing a boost leak test. Just to see or eliminate if that is THE problem, or at least part of the problem. Is your car running rich? (black soot shooting from the muffler, bad gas mileage?)

After you have done that, let us know the results and we can diagnose from there.


http://www.vfaq.com/mods/ICtester.html

 

[RSTurboFWD90]

Have you pulled your ECU and looked for leaking capacitors? My stock '90 Turbo was having the same surging and it turned out to be the ECU. No codes or CEL, right?

 

[PSITSI]

The gas mileage is great, not running rich at all. I haven't had a chance to check the computer. Wasn't sure if that was even a possibility. Thanks guys.

 

[PSITSI]

Have you pulled your ECU and looked for leaking capacitors? My stock '90 Turbo was having the same surging and it turned out to be the ECU. No codes or CEL, right?

Nope, no codes, no CEL. Was yours surging at cruise speed also?

 

[LeroyBKR]

Im having a similar problem.. Car at normal driving has a hesitation/bogging but at wot the bogging is gone.. I already did a boost leak test, changed the isc and tps, new spark plug wires, spark plugs, and changed out the coil pack. Running out of ideas, next going to check the timing.. ANy ideas?

 

[Eastwood95]

You're not venting your Blow Off Valve are you?

 

[PSITSI]

You're not venting your Blow Off Valve are you?

Nope. Recirculated. Like I said, bone stock. However, I *might* have found the problem. My buddy was following me on the interstate, and he said that when I decelerated from a high RPM, I was shooting red-hot chunks of catalytic converter out of the muffler. So, sounds like that is junk. I am working on getting that taken care of. I will let you know if that fixes it.

 

[RSTurboFWD90]

Nope, no codes, no CEL. Was yours surging at cruise speed also?

Yes, only at cruise. It was very bad when cold and less evident when warm. The symptoms worsened over the few months it took me to finally pull the ECU and send it for repair. I had tested and replaced just about every other part. Plugs, wires, coil, power transistor, fuel filter, TPS, ISC. None of these fixed the surging.

As any Wiseman here will tell you, if you have not checked the ECU for leaking capacitors, then you are asking for trouble. If they aren't leaking, the WILL leak. I should tell you that I had to use a magnifying glass to see the leakers on my board. It was barely noticeable to the naked eye. Anyway, after I have the ECU repaired, I have had no problems.

Your cat may be cooked but still check the ECU. If for no other reason you will know it's condition.

 

[PSITSI]

Yes, only at cruise. It was very bad when cold and less evident when warm. The symptoms worsened over the few months it took me to finally pull the ECU and send it for repair. I had tested and replaced just about every other part. Plugs, wires, coil, power transistor, fuel filter, TPS, ISC. None of these fixed the surging.

As any Wiseman here will tell you, if you have not checked the ECU for leaking capacitors, then you are asking for trouble. If they aren't leaking, the WILL leak. I should tell you that I had to use a magnifying glass to see the leakers on my board. It was barely noticeable to the naked eye. Anyway, after I have the ECU repaired, I have had no problems.

Your cat may be cooked but still check the ECU. If for no other reason you will know it's condition.

I will check it out. It is something I had planned on anyway. Thanks

 

[v2ner]

Your cat may be cooked but still check the ECU.

Symptoms of a clogged cat are as you've described more noticeably hard start up. They are also known to backfire all the way through the intake filter as well when you try and start it up.

Gas stations who have poor maintenance will have water in their gas causing the cat to be clogged even faster.

 

[PSITSI]

So, I have a rebuilt Eprom computer lined up for my car, but I have a question. Someone told me that 1990 computers are different and that I will have to switch some wires since the computer I have is from a 92 or 93. Is this true? Anyone know anything about this?

 

[LaN-]

you have to switch around like 2 wires for the ecu swap. check VFAQ.com there should be something on there.

As far as the bucking. My car was doing that and it ended up being the TPS was not connected enough. It was on there enough not to throw a CEL, but off just enough to cause the issue. I popped the hood and pushed it down, all problems went away.

You've already replaced your TPS so maybe its in the cable.

Do you have a logger? Make sure your set right for the TPS

I'd start with the CAT first since its a known issue and go from there.



Just to clean this post up a little can you do an updated check list of what you have tried?

Palm Logger -

Replaced CAT -

Checked TPS cables -

Check CAPS on ECU -

Boost leak tested -

Venting your BOV - NO

fill out the above and post it back so we can better diagnose the issue.

 

[PSITSI]

I will have to work on that soon. I work 12 hour days, so that pretty much rules out any working on my car until Tuesday. I will post as soon as I get a chance to work on it. Thanks