Hard start - irregular idle?

[Steve Calvin]

I've got a 84 pretty much stock, with a condition where it's hard starting and doesn't want to run when it's cold and even once it warms up it won't idle at the 700rpm it should. It fluctuates but is usually around 900-100 in drive.

I've replaced all of the normal things for a tune up, o2 sensors, cleaned the TBI's, air filter, gas filter, plugs, wires, rotor. I had to put a new water pump in it and the pressure told me real quick that I needed a new radiator.
Of course, oil change and filter. Nothing but top of the line parts. No skimping at all. Exhaust is fine (all stainless 2 years old, gutted cat, Flowmaster 50's). I'm planning on replacing the gutted cat with a hi-flow cat in the spring but that's not the problem.

I put an '85 Delco fuel pump in it 2 years ago and the fuel preasure is fine.

I did notice though at an idle I'm getting a constant spray out of the injectors even though the butterfly's are closed and the gas is just kind of laying on the butterflies?

All that's done and I still have the problem described above. I'm thinking the CTS may be the problem. I suppose it could be the 22 year old ECM too.

Ideas?

 

[MBDiagMan]

You say that you replaced the fuel pump two years ago and the fuel pressure is good. Does that mean that you hooked up a gauge while doing all this work and CHECKED the fuel pressure? If so what was it and did it hold pressure for at least a few minutes after turning it off and observing the gauge?

Good luck,

 

[jiangtao]

You might want to check the IAC's! If you do decide to change them, then you should also clean the places where the pintel goes in on the TB's too. I spent almost a year trying to get my '82 back in shape and all it needed was a good cleaning in the IAC tunnels.

 

[Steve Calvin]

Yes, I checked the pressure. 14 lb's steady and holds it. That's why I said that the pressure was fine but I should have posted the number. Sorry.

IAC's.. worth a check. Thanks.

 

[nyernga]

Just got my car back from the shop. I was having an idle "hunting" issue for about 2 months and even after installing a new IAC, complete tune up and adjusting the TPS it still would idle rough and stall when it was warmed up.
Turned out to be the O2 sensor. My mechanic replaced that and reset the idle settings and the car idles fine now....

Len

 

[Steve Calvin]

Thanks, I did a complete tume up which included both O2 sensors. I'll replace the IAC too.

I'm going to get some more diag. tools over the winter and get back at it in the spring.

This car *will* run like it did before or... well.. it will ;-)

 

[MBDiagMan]

It sounds like there might be some temporary budget limitations involved. Believe me, with a kid in college I understand that feeling perfectly.

When you can free up a few bucks, get a fuel pressure gauge. They are not too expensive. With the gauge installed, turn on the key without starting the engine and observe the gauge. If pressure does not come up to 9-13 PSI and hold for at least a few minutes, then the problem is in the fuel circuit. Post the results here and we can pick up the troubleshooting from there.

Even if it is Spring before you post the results, it will bring the post to the top and someone will see it.

Good luck,
Doc

 

[Steve Calvin]

Nope, no budget problems at all - I just don't like workin' on it and freezing while doin' it.

Fuel preasure is fine.

 

[MBDiagMan]

Okay, I don't blame you. If you don't need the car, there's no reason to freeze your fingers.

Does the car run out okay on the road and rev on up with power?

Have a great day,

 

[kevman]

I always thought the '84 only had one O2 sensor.

 

[Steve Calvin]

Okay, I don't blame you. If you don't need the car, there's no reason to freeze your fingers.

Does the car run out okay on the road and rev on up with power?

Have a great day,

*most* of the time. That's whats confusing me. Sometimes it runs absoultlely great. Others, like if I nail it around 20-40mph, it may choke, or may take off like it should. That's why I'm wondering about the ECM?

 

[jiangtao]

I am just wondering, but when you cleaned the TB's did you adjust them with a water meter? If it isn't the TPS then you might have to tune the TB's.

 

[Steve Calvin]

I am just wondering, but when you cleaned the TB's did you adjust them with a water meter? If it isn't the TPS then you might have to tune the TB's.

Yeah, I did but may need to re-check it. Thanks for the idea - I s'pose I coulda screwed it up.

 

[ltmark]

I have an '85 and fought the idel and hard start for some time. I read my shop manual and messed with all the sensors until I knew all the settings and what they did and relied on for months. I my hard start ultimately turned out to be the coolant sensor. The one at the front of the block, NOT the temp gage sensor. The sensor thermister was bad and would read 2volts when cold. It's supposed to be 5 volts when cold and the 2 volts told the ECM that the engine was already warm when starting. I have jurry rigged it for now, because the sensor pigtail is bad and finding one has been a nightmare!

I hooked the sensor wires to the MAT sensor wires, since the MAT sensor sends the same voltage when cold and lowers in the same manner as it warms up!

I personally think the engineer that put the coolant sensor at the front of the block in a spot that is very difficult to get at is probably the same engineer that designed the access to the #8 cylinder.

 

[MBDiagMan]

I have an '85 and fought the idel and hard start for some time. I read my shop manual and messed with all the sensors until I knew all the settings and what they did and relied on for months. I my hard start ultimately turned out to be the coolant sensor. The one at the front of the block, NOT the temp gage sensor. The sensor thermister was bad and would read 2volts when cold. It's supposed to be 5 volts when cold and the 2 volts told the ECM that the engine was already warm when starting. I have jurry rigged it for now, because the sensor pigtail is bad and finding one has been a nightmare!

I hooked the sensor wires to the MAT sensor wires, since the MAT sensor sends the same voltage when cold and lowers in the same manner as it warms up!

I personally think the engineer that put the coolant sensor at the front of the block in a spot that is very difficult to get at is probably the same engineer that designed the access to the #8 cylinder.

Yeah, and that engineer will probably be running the Chevrolet Division before too long. I'm sure that they get extra high review ratings for making things hard to work on.

Glad you nailed down the problem.

Have a great day,