here is my problem;

my car has extensive mods, fast burn heads, mini ram, 406, headers, no cats, aftermarket cam. i also have a custom chip from fast chip.

the car runs great when it's cold. when it warms up is the problem. when the car is warm it hunts for idle, or surges from 800 rpm to 1000 rpm. when i rev the engine and hold it at a higher rpm it decelerates on it's own and then it bounces back to where i was holding it at. this problem also occurs when i'm driving the car on the highway. i'm thinking that the roller tip rockers are sending a false signal to the knock sensor and pulling timing out. this only occurs when the engine is warm up.

is there a way that i can help the knock sensor not hear so much from the rockers by putting insulation around it? should i try to take it off and put it some where else? i do not have a scanner or a way to check engine parameters. the only tunning tool i have is a code reader from Kragen's, and a wide band o2 sensor. i also don't have the money right now to buy a scanner or data logger for a new chip.

is there a way that i can trick the computer to just run like it's cold? is this open loop? any suggestions are appreciated

 

one more thing, i'm looking for a temporary solution until i can get some software and cable to data log and eventually get a new chip burned.

 

my alternator is new and charging.

 

Unplug the O2 sensor.

You could also plug in a dummy O2 sensor (not installed) if you want to avoid setting code 13.

This will keep you in open loop since the O2 sensor will never go "ready".

As the car warms up, a few things happen. The open loop target A/F ratio will begin lean out as a function of coolant temperature and approach 14.73:1. The target idle rpm will also decrease to whatever target idle is programmed in. 14.73 is also the closed loop target A/F.

In closed loop, you have the advantage of O2 sensor feedback to correct the mixture to the target, but this ability is limited. Normally closed loop should run smoother unless you're hitting the limits of compensation. The ecm can add more fuel when lean than it can remove when rich.

My guess is that the 800-1000 rpm surge is caused by spark advance differences between these rpm values and the resulting effect on the engine's torque output due to the changing spark. The mixture is also changing but this affects torque to a lesser extent than the spark.

For a stable idle, you want the torque vs rpm for a given airflow to remain relatively stable since the airflow is the only controlled variable. If the torque is changing independently of the airflow then it will surge.

Only the airflow is controlled by the IAC and it is relatively slow to act.

I would say the spark table needs some work, or the idle needs to be adusted to put you into a more stable region of the table to get a more predictable response from the IAC control.

Adding some inital timing and increasing the min air adjustment may help in the meantime, until you get the tune worked out.

 

This has nothing to do with the knock sensor. If it's knocking at idle when warm, then it's knocking at idle when cold, probably moreso.

99% of the time a problem that starts when it enters closed loop is bad O2 sensors.

If you can't get the proper tools to diagnose it yourself, then take it to a mechanic who can.

 

where is the fun in this, i have gotten this far on my own and with the help of the forum.

it has a knew o2 sensor. i will try to unplug and see what happens. thanks tequila boy. any other suggestions?

 

i tried running the car with the o2 sensor unplugged and it ran well but it felt like i was missing about 100 horsepower. i liked that it was not running rich and that throttle response improved slightly. it also did not hunt for idle and the surging feeling at highway speeds also went away.

when i dropped the hammer was the problem. it felt really slow, down on power.

i reconnected the o2 sensor