Ok, for sometime I have had a rather high idle of about 1500 rpm. Yesterday I charged my AC system and kicked it on. I now have nice cold air and a 750 RPM idle. I know the compressor load will pull the idle down, but going right to 750 rpm doesn't make sense. My car idles perfectly and drives perfect under load with the AC on. But here comes the weird part. I notice very light bucking and hesitation while I am driving on the highway or I am just cruising with extremely light throttle. I checked my AFR's from my O2 sensor (Apex'i turbo timer) and I noticed that when it is bucking, my O2 sensor voltage is at .01 and my AFR is reading 20.0. Could a faulty BAC and a bad O2 sensor cause this idle / hesitation thing. I don't know where to start troubleshooting this.

BTW, when I kick off the AC my idle jumps right back up to 1500 rpm. This is a somewhat recent development but it hasn't worried me enough to actually sit down and start tearing things apart yet. I am getting ready to install a DP and MP and flush the coolant while changing the thermostat and alternator so if it isn't to serious, I'll fix it then. Anyone's input would be lovely.

Also, my gas mileage is horrid. I think I am averaging about 14 miles to the gallons and that is with ALOT of highway driving with little to no boost everyday (I'll admit that I do redline it once in a bit though, but not enough to explain this mileage.)

So, any guesses?

 

First, I'll tackle the highway problem. As the compessor cycles on and off the engine rpm's will change, small engine with very little torque, so hopefully this is what you are feeling.
If the high idle is something that started recently, and the car has no other noticeable problems, check the setting, and resistance condition of the TPS.

 

The highway problem isn't the AC cycling on and off. It is hesitating or misfiring. If i give it just a little more gas, and by little I am talking like maybe 2 - 4 mm just to crack open the secondary throttle plates a hair, the hesitation goes away and I have a noticeable surge in power.

The TPS reads perfect with no dead shorts. I get the correct numbers across the entire range.

Anyone else have any ideas?

 

Anyone else?

 

I also have the same problem and have recieved no reply I am checking TPS O2 sensors and everything this weekend othewise I don't know what it could be. 1500 rps steady. I have no A/C so I know it isn't the problem. What kind of smoke is coming out the back regular or blue or white??

 

I'm havin same problem with bucking/hesisyaion ha. At slight throttle it bucks back and ourth

 

check your injectors and tps. i had the same problem.

 

Well I had my tps checked it and it was good. Wat should I check on injectors?

 

My TPS is golden, no smoke out of the back.

Thinking about it, I think I will check the injectors.... nevermind. I'll just go ahead and pick up some 720's.

 

I have the same problem of idling really high at 1300 to 1400 rpms. When I put on the AC it stalls, and sometimes it hunts for an idle at 500 to 700 rpms. I am really confused, brand new rebuilt with 6 grand on the clock, clean injectors, new vaccuum lines, adjusted TPS, brand new wax seal thing, and the BAC doesn't work. Any ideas... Sorry to steal your thread.
Sam