Hesitation when warm under 2000 RPM

[red-in-la]

All of a sudden it happened:
1. When hot, pushing down of gas peddel as normal = major hesitation and pinging until you can get to 2000 rpm. Then all is well.
2. When cold all is well.
3. Above 2000 rpm hot or cold, all is well.
4. When applying gas peddle SLOWLY until 2000 rpm all is ok.

What we have done:
1. checked EGR valve
2. checked fuel pressure (36psi, 41 with no vacuum)
3. checked injectors (getting correct electrical inputs)
4. changed water temp probe. If we disconnect this one with another one that is cool (not in the water, just a changing the wire to another probe.) the idle increases and the stumbling stops; until the other probe gets warmed up.
5. alternator checked
6. cat checked
7. vacuums checked
8. throttle position sensor voltage checked
9. gas is fine
10. fuel filter is fine
11. newer wires and they are fine
12. plugs are good and show good color
13. timing belt was changed at 140k with water pump, etc.
14. not cell lights
15. no problems on computer
16. no problems shown on cumputer we hooked up to the car.

I'm sure there's more, but I'm forgetful at this point.
My mechanic and I are about ready to....
This is all happening to an early '93 with 165k miles. It's had good maintence and oil changes.

2000 rpm seems to be the magic number here, for some unknow reason.

HELP,
Regards....

[Brian R.]

Did you check the injectors for spray pattern? Clean them?
Checked fuel flow?
Checked ignition timing?
Timing belt installed correctly (not off by a tooth)?
Thermostat good (not off-temperature)?
Radiator and engine full of coolant - no air trapped?
Radiator cap holds pressure?
Check compression?
Check distributer cap for cracks or arcing? - bad rotor?
Check intake manifold vacuum at idle and off idle? - bad manifold gasket or leak in hoses?
Defective knock sensor?

[red-in-la]

Brian, thanks for the input.

Originally Posted by Brian R.

Did you check the injectors for spray pattern? Clean them?
Checked fuel flow?
Checked ignition timing?
Timing belt installed correctly (not off by a tooth)?
Thermostat good (not off-temperature)?
Radiator and engine full of coolant - no air trapped?
Radiator cap holds pressure?
Check compression?
Check distributer cap for cracks or arcing? - bad rotor?
Check intake manifold vacuum at idle and off idle? - bad manifold gasket or leak in hoses?
Defective knock sensor?

In order:
No. just went with the fact that they were getting electrical signal
Yes.
Yes.
Yes. Timing belt was done 25k ago.
Yes.
Yes.
Yes.
Yes. However, I am going to go buy a new cap & rotor tomorrow just out of general principals.
Yes.
Unsure. I'll look into knock sensor.

The key things here are the 2000 rpm and then smooth running and this just started happening out of the clear blue sky.
Plug wires were just done 22k miles ago, June '03.

Regards

[Brian R.]

4 or 6 cyl?

Last straw, check timing belt to make sure it didn't go bad - jump a tooth or loose a tooth. Correct tension on timing belt? - driving water pump.

[red-in-la]

4 cylinder. Sorry, got all the other info in.

Regards

[red-in-la]

The puzzle continues.

Changed wires, cap & rotor. No luck.
Put a reader on it for the onboard computer. Everything works.

Put it on a smog machine and it's showing rich when it sounds like it's trying to destroy itself. Sounds like someone in there with a hammer beating on it when the engines under a load.

So the computer is opening the injectors and dumping in lots of fuel (pressure is good) until it finally gets over 2k rpm. Stinks from tailpipe emissions when this is happening. Hydrocarbons or NO something like that.

After 2k rpm and running smooth it can pass smog with no problems.
Going to try and put in a different computer tomorrow.

Regards

[Brian R.]

Rich mixture and pinging don't go together. A puzzle. Test the other sensors (outside air temp, oxygen, etc) for correct operation.

[red-in-la]

The distributor is now being suggested as a possible problem.

Apparently the distributor on the this car has all sorts of goodies in it that could be messing up.

Trying to locate a "loaner" as they are ExpensivE. Found new one for $295, but non-returnable. Junkyard ones are few and far between. Dealer wants something like $600 for one.

Regards

[red-in-la]

Still wondering why the car drives fine though, when we disconnect the "hot" hot water sensor and attatch the wiring to a "cold" hot water sensor?
As long as that sensor is cold, the car runs fine.

Regards

[Mike Gerber]

red-in-la,

Had a problem similiar to this on an old 86 Camry with a 2SE engine. It ran fine when cold for a few moments after you first started it in the morning. Then, after it would warm up, it would buck and sputter under acceleration until you reached a steady speed, where it ran pretty well. Come to a stop and the process started all over again. No check engine lights and no codes were present. I tried everything until a friend, who was an ex-Toyota-tech suggested trying another O2 sensor. We shut the engine off, disconneted the existing O2 sensor connector, hooked in another one that wasn't exactly right for the car but fit the connector and just hung it over the fender. We started the car and went for a ride this way and the problem was gone. We then got a universal sensor, spliced it in to the existing sensor wiring and that permanently solved the problems. It seems, when starting a cold engine, the O2 sensor is out of the loop until it reaches a certain operating temperature. That's why with a defective O2 sensor, the car ran well when cold. I can't explain why it didn't throw a code but it was the problem. If your o2 sensor is original and hasn't been changed, it might be worth replacing it, even just as general maintenance.

Good luck with the problem.

Mike

[Joe W]

I've got to agree with Mike as I have run into this myself.The O2 sensor is considered a maintenance item anyway.

[Parmenides3]

What's the recommended interval for O2 sensor replacement?

[red-in-la]

Will be at the mechanics bright and early Monday morning with an O2 sensor.

Wish I could get to the car today and try it.....

Going to be interesting since all the voltages and checks were good on the O2 sensor.

Will report back Monday.......

Thanks

[red-in-la]

Damn, totally bummed. The O2 sensor wasn't the problem.

After the car warms up, we were back to the same old problems as outlined above.

Still trying to get a loaner distributor

*sighhhhh*

Regrards

[nmikmik]

Did you try that new computer? or may be there is any way to reset your ECU, like 100% reset? Not even sure what I am talking about, but it does sound like a computer problem. My be it does not give you any codes because it can’t i.e. that part of the computer is broken as well at the one that controls rpms at 2000 ??? I am sure lost, at least in the good company, sorry about your trouble