Bucking for a couple of minutes after start

[j_norton]

For about 6 months my 1990 Eagle Talon Tsi AWD will buck
after it is started when put in gear, even with light throttle.
I wait a couple of minutes, the idle comes down to 750 and it
will now run just fine. During that initial time I think it is running
rich because I can smell the unburned fuel in the exhaust.
As long as I do not turn it off, you could not tell that there is something
wrong. If I turn it off and start it up within a couple of minutes, it is fine.
But if I turn it off and wait about 5 minutes, it will buck again for the
mandatory couple of minutes and it again runs just fine.
I took it to the Chrysler dealer and a local speed shop and they could not
find any problems.
Has anybody seen this problem before ?
What can possibly cause this bucking for a few minutes after start ?
Thanks for any ideas.

 

[luv2rallye]

Vapor lock, probably fuel pressure solinoid - see: http://www.dsmtuners.com/forums/newbie-forum/217349-vapor-lock-hot-start.html

 

[j_norton]

Thanks luv2rallye for your response.
In cfisher thread regarding vapor lock, he only had problems when
the car was hot. I have this bucking for a couple of minutes even after
a cold start when the car sat overnight in the cold New England Winter.
Could you get vapor lock just when the car starts stiff cold.
Thanks for your thought.

 

[luv2rallye]

No, pretty unlikely. I didn't realize you also had it when stiff cold, sorry. By bucking do you mean idle surge? If so see http://www.dsmtuners.com/forums/articles-engine-fuel/191137-how-fix-your-idle-surge-problem.html.

 

[j_norton]

I do not think it is idle surge.
When I start cold, the idle will rev to about 1500
and is fairly steady as it comes down slowly to 750.
That part feels normal. But if I put her in gear within
2-3 minutes after the start it will lurch forward and stop,
lurch and stop… That is what I mean by bucking.
The engine never dies when this happens but I do not
ride it this way for too long because it feels like sitting
on a bronco. After the few minutes of idling, it runs just fine.
In 2004 Mark_l posted that he has a similar jerky problem
that caused a head rebuild because the valve guides were shot.
Any chance that this is my problem ?
Thanks for your help.

 

[GRAVEDIGGER]

When's the last time you replaced the plugs and wires? Sounds like an ignition problem to me. If you haven't done so in a while or don't know the last time it was done I would replace them and see what happens.

 

[j_norton]

Hi GRAVEDIGGER. Chasing this problem for the last few months,
I replace the plugs and wires, cleaned the throttle body and
intake manifold runners, ran injector cleaner, replaced the MAF
and tested other sensors. No Luck.
I am focused on the fact that the problem goes away every
time after idling for about 2-3 minutes.
What could do that ?

 

[johneclipse]

have you checked your fuel pressure on start up? could be bleeding off pressure then takes a minute or two to regain it. My 90 does this due to a bad fuel pump install.

 

[luv2rallye]

Did you test the ECT sensor? A bad one would make it run rich while cold.

 

[luv2rallye]

Engine Coolant Temp sensor - the 2 wire one near the thermostat. Test by measuring resistance of it disconnected.
32*F - 5100-6500ohms
68*F - 2100-2700ohms
104*F - 900-1300ohm
176*F - 260-360ohms

 

[rare1]

Did you fix this problem?I'm having the same problem.

 

[GsXdSmKingGsX]

Did you fix this problem?I'm having the same problem.

Do you have a wideband guage?

 

[rare1]

No!Check codes and get airflow and ignition faults

Figured mine out.The connector going to the coilpack has play in it.I guess the rubber insert to keep water out is worn out.

 

[j_norton]

SOLVED - It was a failed part on the PCM.
Thanks to the local Ex-Mitsubishi (now KIA) technician
who noticed that the computer was getting varying values
from sensors such as O2, pressure and temp. A common
point for those sensors is the PCM. After the module was
repaired, the car runs as good as new.
Thanks to all who posted suggestions.