Driving w/ TPS disconnected?

My RPM's were bouncing around -/+ 200 while at 50-60 mph in my 91 4.0. After doing some searching on here I found that the TPS might be the culprit. I disconnected the TPS and drove my xj to see if the problem still occurred. It did not. I was wondering how long I can drive with the sensor disconnected. My military pay doesn't come in until next week. Is there any problems with running this disconnected for that long or even longer? Thanks.

Are you sure that you mean TPS-throttle position sensor? This tells the computer what the throttle opening is and I see no way it could run without that sensor. Maybe you mean the other gizmo on the throttle body, the idle bypass thingy, that increases the idle speed when the engine is cold? If it is the latter, as long as it is warm, you shouldn't need it.

Fred

The engine can run without the TPS connected. It will use info from the MAP sensor and O2 sensor to adjust fuel supply. Throttle response will be affected. I'm not sure on long term issues driving with the sensor disconnected.

Warning, follows is a noob post - take FWIW. This noob is an old guy who used to fix cars for a living back when everything except Volvos still had carbs, but has moved on to construction equipment

I dunno about the newer year but my 87 is having some sort of problem with the interaction between the TPS and the IAC. With both connected the idle speed goes into the stratosphere. Unplug the TPS and the thing idles down right where it oughta be. Runs sort of okay that way but driveability suffers because I get a stumble when taking off from a stop. Better driveabilioty resulted from reconnecting the TPS after startup and disconnecting the IAC while running at a more normal idle speed. I get an unchanging air opening that gets an idle that's a bit slow cold, a bit fast hot, but no stumble. Still sorting out my problem here, the ultra-high idling thing seems to be fairly common but everybody on every forum seems to have a different opinion about the likely cause (I would love to have a complete engine control electrical schematic if anyone has one).

But if I'm correct, the Chrysler designed EEC will probably go into limp-in if any sensor is out and will run, but like pure crap. The Renix setup seems to behave differently, and tries to work the best it can with what it has. Do know it absolutely will not run without a MAP sensor though (note to self: grab a spare next time at the pick-a-part).

Well after taking the xj for a more thorough test drive this morning, the rpms are doing the same thing. I guess I will hook it back up and start looking for a fix elsewhere.

Auto or manual trans? Torque lockup shifting in & out, or maybe just starting to slip? Give the drive oil a good sniff.
Fuel pressure might be getting a bit low.
Also it's summer. Sometimes an A/C problem (or even normal operation - can't feel it coming on in my 454 Suburban, but sure can in my 6 cyl Jeep) can manifest itself as a surge. My wife's minivan was doing that, she thought the tranny was going out (that's what she always thinks) but it was just too much pressure building up, expansion valve plugged or something. Gotta fix that some day (she knows what to do to get that done).

Dave-"Give the drive oil a good sniff."

What ecaxtly am I going to be smelling for? Burnt type smell? Thanks a ton.

Yeah sniff for that burnt smell. If you're getting a lot of slippage & the clutch linings are starting to burn it'll stink pretty good - so you'll know something's going on in there, failing. Still you could have a converter lockup shifting in & out - "hunting" it's called, and not generally a real serious problem. Wouldn't think that would be normal at the road speed you're getting the RPM surge in, and quite honestly one more familiar with the AW4s quirks would have to say if that's even a probablity - I just know it's a thing that I have seen in other vehicles with locking torques.

Dave,

You might want to check the Yahoo group, Strokers(I know, I know). The group is about stroking the 4.0 liter engine. At one point they had a file available that is the manual for the 1987-1990 Renix fuel injection system. It's fairly useful. All the Yahoo groups have sections where members can access files that other members store there. It's a pretty simple system, just as easy to understand in general as a carburated system. I haven't run across anything that explains your idle problem, however.

Fred

Hi Fred, Actually I got a PM from another member here right after I posted that query and got a download for a 100 page manual on the system that was very helpful. Will have to check out that group though, thanks for the info.

It was a flaky TPS and degreasing the engine finished it off bigtime. Bought one at the closest junkyard for not much more than nothing and it purrs like a kitten.