truck jerking

Hello, I am new to this site. I have a 1988 Comanche 4.0 engine 5 speed manual trans BA10.
I have a problem with it jerking and bucking. In the morning I drive 7 miles with no problems. I stop for about 45 min and this is when the problem starts. I jerk and bucks I only go for maybe 1/2 mile. When I drive it for more than a mile the problem seems to go away. This problem seems to come on when we have a nice day. When it's a cold day it does not act up.
I have changed the fuel pump and filter, O2 sensor, TPS, cap, rotor, wires, plugs & air filter. I have also changed the manifold gasket. In fustratration I put it in a shop. They cleaned the throttle body and IAC motor. But the problem came back. They then changed the fuel presure regulator and the coil. Again the problem came back. They have had it for about a month but it has been cold so the problem would not show itself. Now they have told me that they tryed a new cps still the problem persist. They also say that they can't get it to show a code. By the time the problem shows itself and they put it on the tester the problem corrects it self. Please help
Thank You

I would lean towards checking the throttle body again. My renix was forever cloging up. I figured I was clearing it out every two or three months. Would feel like It was chokeing, clutch in and rev it up and that would clear it out a little. Search Ecomike Renix. That guy is the Renix master and his threads are full of really great info.

Jaime01 said:

I have a 1988 Comanche 4.0 engine 5 speed manual trans BA10......They also say that they can't get it to show a code.

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the next time you're speaking with them, ask them how they're checking for codes-- '88 Renix (Renault/Bendix) ECU doesn't generate trouble codes that can be retrieved.

Before you begin diagnosing problems on this vintage vehicle, it is necessary to refresh all engine ground connections. "Clean, shiny, and tight" has solved more driveability problems on Renix vehicles than anything else.

-- Battery, ECU, and engine controls all ground to the block on the passenger side at the dipstick tube mount.
-- braided ground strap from firewall to cylinder head provides ground path from chassis to block.
-- additional circuits that have history of failure run through a multi-wire plug above the brake booster/master cylinder (C-101 plug). A thorough cleaning of that connection is imperative to solid troubleshooting.

Are you actually paying this shop to work on your Jeep?? If so, and you can't or don't want to do the work yourself, take it without delay to another shop. They are either ripping you off or are inept, or both.

Diagnosing most every problem on a RENIX can be done with a digital multi meter (DMM) or searching for vacuum leaks at key components of the motor. Don't let this shop do anymore work on your Jeep.

There is all kinds of information for everyone from a novice to an expert on this and other forums. ComancheClub.com is also rich with info.

The mechanic did say that the truck does not hold a code and that is the problem he is having. By the time he puts the tester on it when it does act up the truck fixes itself. He also mentioned the the tester he is using, I forgot the name of it, but it's the one that the FMS says to use. I used my multi meter on the sensors and could not find a falty one according to the FMS.

I also posted this on Comanche Club and was told I might be a heat soak problem. But I could not figure out what might be getting heat soaked. Nothing has been changed before I had this problem. Everything that has been done to is was to try and fix the problem.