67tripwr

When it starts warming up it starts running like hell. Any ideas?????

WW7

Well since it doesn't start running bad until it goes into closed loop it may be something associated with one of the sensors. When in open loop it runs off a set of perameters in the ecm, when it goes into closed loop(160 to 170 degrees) it starts using the sensors. There are a lot of things it could be , O2 sensor, temp sensor. The best thing you could do is hook it up to a scanner and see what readings you get.We really need more information on how its running before anyone here could give you some ideas about what it could be.WW

67tripwr

Thanks for that info!!! I will stop by the shop tomorrow!

mechguy79

Harsh20

could be as simple as cleaning the throttle body. could be some build up around the butterfly not letting enough air in at cold start.

ex-x-fire

Check your fuel press. & make sure it holds it (when key is off)
Check your grounds, vacuum hoses, & fluid levels.
Make sure the egr valve isn't sticking.
Remove your coolant temp senser, when it is at room temp. the resistance should be 3400 olhms. Place the tip of the sense into hot water or the hot coolant of another car, at about 200* the resistence should be about 200-190 olhms. If the resistence stay up the senser is bad, what a bad cts does to your motor is make it run VERY RICH. Good luck.

AGENT 86

Ohm testing your injectors when hot, should be on the list, too.
http://forums.corvetteforum.com/c4-t...questions.html

CorvetteMike2024

You need to replace your fuel injectors.

Corvette Mike

5abivt

I believe the first response is what i would chase. If it starts cold then goes bad that means one of the sensors is sending bad info to the ecm. When you first start the car it does not read all of them.

Pull off some of your sensors make sure they are clean, and plugged in .

ddahlgren

Describe runs like hell? without even a cheap scan tool you are just hopeing to stumble across the problem.

96GS#007

Bad injectors. Ohm check them hot and cold. My '90 did the same thing. Started fine and as soon as it went closed loop it ran horrible.

67tripwr

How about bad MAF sensor? That could be a probe as well?

gmboileau

I believe a 91 has a MAP sensor instead of MAF sensor. As suggested check the OHMs reading of the injectors both hot and cold. It's easy, takes a short time and no cost.

67tripwr

In regards to resistance testing the injectors. Each injector has a filter screen, and they can get clogged up with dirt. Will the resistance test reveal that? I don't see how?

SunCr

No - but there isn't a flow restriction problem because more fuel is provided when it's cold and if it were restricted; it'd run like crap when it's cold too. The temp signal for fuel delivery is from the Coolant Temp Sensor and you check it with a scanner; ideally, after it's sat overnight. It should be around ambient and close to the Air Intake Sensor. After starting, it should rise to the thermostat; drop back a few degrees when it opens; and then rise again to the threshold for main fan operation (226 for this Year). Assuming it checks out, look for something else - like weak injector coils. Each should ohm out at 15 ohms or better hot/cold.

ex-x-fire

A way to look at it is the eng. coolant temp. senser does what the choke spring does on a carb. It just does it much more precise when its working correctly.

H P Bushrod

Check your ignition module also.

Millah

my 89 does the same thing. runs great till warmed up. I ordered a new temp sensor to see if that works first.