Strange drag feeling on highway

99 XJ 4x4 Stock 200K on body

I'm trying to determine if this is a a/c compressor going bad or something else. When I'm on a long highway drive, after about 20-30 minutes, i will intermittently get a drag or pull from something which feels like i'm quickly tapping and then letting off on the brake. It will sometimes happen ever few minutes, and sometimes several times in a row, every few seconds. I turn off the a/c and it usually lets up but every so often I believe it happens again even with the a/c off. I would think if it was the a/c I would hear a belt squeal, but I do not hear anything.

Some other symptoms that may be related, or may not be:
I do have some vibes and some play in the steering
I get some squeaking when I turn
The motor feels a little down on power right now and idles a little rough

Any thoughts? Thanks so much!

Also, I only get about 15mpg, no matter if its city or hwy.

Possible cps failing or dirty.

I've had CPS issues before, but i'm not sure this would be caused by CPS. It definitely feels like a physical drag and not a loss of power when this happens.

You mentioned it feels like tapping on the brakes. That would make me assume the engine is possible cutting out for a split 1000th or so of a second.

If it feels like the brakes are applied and slowly let off over the course of 1-2 seconds, then that is different.

I guess that could be a possibility. Any way to test?

There is a way to test it. I have no idea how.

My way is to replace it, but obviously that's not the right thing to do. Start by pulling and cleaning it.

Been in any mud or deep water lately?

I recently picked this one up and haven't had a chance to really get into it yet. No, I haven't done anything other than drive it down the road. The motor was taken out of a donor with 145k on it, but trans is stock and so has 200k on it. Perhaps they could have messed up the cps during install, or its just old.

There is a possibility of a belt-driven accessory that is going bad dragging down your fuel mileage, and I have personally experience instances where A/C compressors on long-dead systems would suddenly "engage" and stall out vehicles.

That said, from your description, it still could be a fuel/ignition interruption.

If you suspect the AC compressor, it's really easy to eliminate this by unplugging the wire on the receiver-drier, which is on the firewall. If you pull that plug, the compressor will not engage. This won't, of course, eliminate a bad compressor pulley bearing, but it's a start.

Don't I accomplish the same thing by just turning the a/c off?

phil04 said:

Don't I accomplish the same thing by just turning the a/c off?

Click to expand...

Probably, except when using defrost, when it is always on. But if you want to eliminate all possibility of a control malfunction, it's really easy just to unplug that wire and be sure.