Another odd idle problem

[RobertK]

In the process of working out all the little quirks to my brother's engine the only 2 problems he has right now is.

1. Sometimes when coming to a stop the car wants to idle at 1000-/+RPM but if you tap the gas pedal the idle goes down to 800RPM.

2. About 60% of the time when you go to start the car it starts and then dies about 2-3 times before starting up and idling on it's own. Sometimes you have to give it a little gas to do this.

Now the weird idle problem is more recent but the problem with it starting a dying has like that before we rebuilt the engine and dropped it back in. The only things I can think of that would cause the startup and die problem are the fuel pump, fpr, or the fuel filter.

We've replaced these parts already:

AFM
ICV
O2 Sensor
Plugs & Wires w/ Pulse Sensor
New Bosch Cap and Rotor
17.5lb injectors - All Good w/ new o-rings
All new vacuum hoses
New intake boot

[thereisnoyun]

mine idles the same

my engine idle the same, but it doesnt die or nothing. It sometimes goes to 800 but stays at 1000 times... wierd.

[taylor89]

Do the symptoms vary when it is either a cold start or warm start?

[RobertK]

Usually does it more often when it is cold.

[jlevie]

The idle problem when coming to a stop could be a binding throttle cable, sticking throttle body, or on cars so equipped a bad Idle Control Module. The starting problem on a cold engine could be from low fuel pressure (weak pressure pump, weak or failed transfer pump on cars so equipped, clogged filter, bad FPR, etc). Or it could be an intake leak. A pressure gauge attached to the supply to the fuel rail will tell if there's a fuel pressure problem.

[RobertK]

We swapped out the fuel filter tonight and after some thought I realized my brother's car was never reaching temperature above the 1/4 mark. He had installed a 71 degree thermostat and the fan was set to always on because we had wired it to the heater wire off the O2 relay.

My thoughts were that since it was not ever getting up past the 1/4 mark that the engine wasn't reaching optimum temp and constantly dumping fuel into the engine per the temp sensor readout.

We picked up a 80c fan switch and then wired the fan relay to it instead so the fan only comes on when the car reaches temp. This works however when the car is moving it still rarely gets further than in between 1/4 and 1/2 mark on the temp gauge. Only when idling for a long period of time does the fan kick on right when it gets to 1/2.

On our first couple of test runs the car started up everytime no problem with the new fuel filter BUT a couple of times the car hiccupped. Ever time it did hiccup the CEL flashed for a sec. On our second run the CEL came on and stayed on. The only code being stored is still the 1221 = O2 sensor which is brand spanking new installed yesterday.

WTF?

[HST]

Maybe you should get a 80c thermostat. That is the only reason that I would think that the car would dip below half when it is in motion. Also have you checked to make sure that the oil cooler is not flowing oil through it all the time? I would not think that it would make a big difference but it might. You could always put a piece of plastic or something in front of the radiator to make it less efficient...

[RobertK]

Maybe you should get a 80c thermostat. That is the only reason that I would think that the car would dip below half when it is in motion. Also have you checked to make sure that the oil cooler is not flowing oil through it all the time? I would not think that it would make a big difference but it might. You could always put a piece of plastic or something in front of the radiator to make it less efficient...

I would hope that if the oil cooler isn't flowing that it would set off the oil pressure dummy light so I'm sure that's not it.

I spoke with my buddy Doug today at work (resident car buff at work) and seems to think it's the ECU since it had weird idle issues before the engine overhaul.

[HST]

I would hope that if the oil cooler isn't flowing that it would set off the oil pressure dummy light so I'm sure that's not it.

No, I mean that if oil is always going through the oil cooler than it might cause the engine to stay too cool. Like if the thermostat in the oil filter housing is stuck in the open position or something, or is not working. I do like the ECU, and with the extra one you got, it would be an easy test. More bastardizing of the bronzit car !!!!!

[RobertK]

No, I mean that if oil is always going through the oil cooler than it might cause the engine to stay too cool. Like if the thermostat in the oil filter housing is stuck in the open position or something, or is not working. I do like the ECU, and with the extra one you got, it would be an easy test. More bastardizing of the bronzit car !!!!!

If anything the oil cooler thermostat would get stuck in the closed position. The engine mush get up to 80C before the oil can which is what opens up the oil thermostat to the cooler. But even when I installed my cooler without the oil thermostat last summer the car had no problems reaching temp and staying there.

I think we built up Preston's M20 too good.