Good Evening All

Well, I spent the winter (off and on) trying to track dwn the cold engine drivibility issue in the '88 Omni (Throttle Body 5 speed). I even broke down and took it to a locally owned (not a chain store) repair shop. There are no fault codes and the the only time it acts up is when the engine is cold. The shop found that my Autolite spark plugs were about 3/16 shorter than the Original Equipment Champions. I replaced the plugs, however the problem is still there.

The problem is that when the engine is cold, it idles like a carburator with a stuck choke. When you accelerate to 2500RPM the motor bucks like it dropped a cylinder. Once it warms up, it runs great.

To day I looked at it again. I tested the fuel pump pressure (the pump is still original w/162K on the clock). Pressure was 15 psi. I checked the timing (12* BTC with the coolant temp sensor unhooked). I then tested the air temp sensor that is located in the top of the air cleaner housing. It would not hold vacuum, The vacuum motor that controls the air door between the pre-heat hose and the fresh air duct works great. (held 20hg for 10 minutes as per the shop manual). All the vacuum hoses are pliable. So, my reasoning takes me to the sensor.

Looking at all the usual parts stores, I am coming up empty. Does any one have a lead on part # 4542765? The book calls it a SENSOR, Temperature. It is about the size of a quarter with 2 vacuum nipples, It is located inside the cover of the air cleaner housing.

A couple of years ago, I replaced one on my '79 Volare. If memory servs me correctly, these items were used back in the early seventies. They were located in the air cleaner and coltoleed the 'door0 between the heat stove and the snorkel.
As all ways, all replies are welcome.

If you do not receive the needed help try here.
http://www.misterfixit.com/autorepr.htm#CATEGORIES

Maybe you have worn valve guides and bad seals? You might be getting oil on a plug. Or you have a head gasket starting to fail getting coolant into the cylinder. Pull the plugs and look at them very closely.

Heres a earlier sensor if it happens to be the same...

http://cgi.ebay.com/ebaymotors/NOS-35141...1d#ht_520wt_941

Cold running issue- could be either "choke" system or a vacuum leak. Do the TBI's have the same isolator problem that the carbed cars do?

Coolant temp sensor, what is the coolant temp sensor reading when cold
Thad

The coolant temp sensor would have it running super rich hot.Ive never seen one that didnt go bad that didnt show the temp to computer as super cold.They did have an injector problem with the early cars.There was a TSB for it.I replaced quite a few injectors on them.Rocky

Good Morning

Let me update what I've done to the Omni to date.
The following parts have been replaced over the course of last year:
Head & head gasket along with the intake/exhaust and head pipe gasket)
AIS motor and Throttle position sensor, cap rotor and wires
Spark plugs (twice)

No plug fouling due to excesive oil or coolant (it does show an over-rich condition which would confirm the cold engine trouble).

The throttle body does sit on a thick spacer (insolater - not the rubber types that the carbed models use. Spraying areosol at the base while running did not indicate any leakage.

The car is driven about 20 to work one way, mostly on the highway. The mileage last year averaged between 30-34. Now it is between 26-29. I realize that winter and crappy gas will take its toll in the mileage area, however, once the problem is correctd it should help.

The link for the e-bag sensor was exactally what I'm looking for.
A big thanks for that.

As always thanks to all of you who responded.

1) Check the coil.

It is in a c*r*a*p location that was done to save money and a poor design to boot. Should be hanging off the thermostat housing. Known for getting cracks near the 2 pin plug. When in doubt replace, a cheap part. I have replaced dozens on 2.2's and 5.2' over the years (same design)

2) Verify cam and distributor timing are spot on, either one off (even a little bit) can cause drivability issues. Distributor timing off as much as 2-3 degrees can make the car run poor. 12 degrees is correct with the car warmed up, at idle and the coolent sensor unplugged.

3) Make sure there is no leaks on the map sensor line and make sure the baro read solinoid (if equipped) is not stuck/leaking. Bypass it if need be to test. Make sure nothing else is on the map line aside from the fuel pressure regulator.

I doubt the problem is the vacuum switch for the heated air door, sounds for sure like a weak coil. When the engine is cold it takes more juice to fire off the mixture and will be enough to push the coil over the edge till the car warms up.

Seen dozens of cars and truck do this with the encapsulated coils.

Good Evening

It is in a c*r*a*p location that was done to save money and a poor design to boot. Should be hanging off the thermostat housing. Known for getting cracks near the 2 pin plug. When in doubt replace, a cheap part. I have replaced dozens on 2.2's and 5.2' over the years (same design)

The coil looks like a standard coil. I don't see a two pin plug, just a seperate (-) and (+) along with the high tension lead and the radio supressor. It is bolted to the right side inner fender. I forgot to mentioned that it was also replaced last fall. (My thought process was the same as yours - weak coil insufficent spark when cold).

The crank/cam and accessory shaft (distributor) are aligned as per the manual. One thought though, with the crank and accessory drive are aligned, the cam is about 1/2 tooth off. I errored on the side of advance.

I checked the map sensor and it is the only piece on that vacuum circuit.

Thanks for the advice.

Good Day All

I believe that the Omni has ben cured of its cold engine drivability issue.

The air cleaner temp senor was by-passed in an effort to trouble shoot the system. When I did this the engine will now stay running when cold and the mileage increased for the upper 20's to 34.5.

I secured another sensor off e-bag, however I might not install it until warmer weather. When cold weather arrives again, I think I'll by-pass it.

It has been a long and winding road, but I think I've reached the end.

Thanks to All who took the time to respond.

Omni

Some of these things will drive you nuts. Glad you have it fixed.