TPS on OBDII Logger Help

I recently bought a 2000 XJ. Since I got it, it has had a problem at idle.

While idleing, about every 30 seconds the motor will get alot louder, like its under load, stay loud for 10 seconds then go back to normal idle. Also when it switches from loud to normal I can hear something like a vacuum diaphragm moving under the dash.

At first I thought this was idle surge, but RPMs barely move when it gets louder, maybe 50 rpm more.

So I hooked up my OBDII logger, O2 sensor cycling good, MAP = 18 inHG at 750 rpm, 20 inHG at 1500, everything looks good except TPS.

TPS reads 17% with foot off the gas and 74% with it floored.

Does anyone have some OBDII readings I could compare mine to, to see if my TPS is bad?

Or know what could be causing my idle problem?

Thanks.

Two things will make it idle like that, first if you have your defrosters turned, both the last two positions do this, on at which point the ac compressor cycles in and the electric fan comes on. The second is the fan clutch is shot and the electric fan is kicking on, does it run hot ?

sounds like a TPS issue. When I monitored the big rigs they were at 0% at idle & 99% at full throttle. OBD2 may be diff, but I don't think 17% with your foot off the throttle is right.

It does not run hot. I have had the vent select knob on defrost since I bought it. Didn't know the AC kicked in, thought hot air was just directed to window. Now I feel really stupid, you don't want to know how long I spent looking for vacuum leaks and loose wires. That might explain the crappy mileage I've been getting too.

Thanks a lot!!!

Ceddy said:

It does not run hot. I have had the vent select knob on defrost since I bought it. Didn't know the AC kicked in, thought hot air was just directed to window. Now I feel really stupid, you don't want to know how long I spent looking for vacuum leaks and loose wires. That might explain the crappy mileage I've been getting too.

Thanks a lot!!!

Click to expand...

The compressor kicks in to dry the air out so it clears the windshield faster... those last two positions, def/mix and def will do it...

Ceddy said:

It does not run hot. I have had the vent select knob on defrost since I bought it. Didn't know the AC kicked in, thought hot air was just directed to window. Now I feel really stupid, you don't want to know how long I spent looking for vacuum leaks and loose wires. That might explain the crappy mileage I've been getting too.

Thanks a lot!!!

Click to expand...

When it "gets louder" you will notice the auxillary fan kicking on and off.

Normal, especially when the defrost or AC is on.

Ceddy said:

It does not run hot. I have had the vent select knob on defrost since I bought it. Didn't know the AC kicked in, thought hot air was just directed to window. Now I feel really stupid, you don't want to know how long I spent looking for vacuum leaks and loose wires. That might explain the crappy mileage I've been getting too.

Thanks a lot!!!

Click to expand...

The crappy mileage is probably your O2 sensor if you have good plugs, wires, cap and rotor, no fancy plats either, the 4.0 likes champion coppers....

I just went outside and checked, RichP you are 100% correct.

Thanks again.

With regard to the A/C coming on, it is a default for in the winter time it allows the A/C to move oil around and keep things "lubed", and it also helps with the force and flow of the air, the only difference is the blend door moves from cold to hot, going from A/C to defrost. This is nothing to worry about it is normal.