renix issues....

Ok this 89 4.0 4wd auto sat for over a year,with a few monkeys working on it. Wasnt getting power to pump,new entire fuel pump unit got it running,did all the ground cleaning , 4 gauge wire to block,fender,truck ran great but wont pass emissions,running rich,cracked header,replaced and now i have low idle issue,cleaned iac but havent had time to clean whole throttle body,new cps,checked tps perfect,know knock sensor is broken but the issue is when i hit 45 mph at 1500rpm starts to stutter and vibrate. Let off gas and get back in her good but when it goes to od? at 1500rpm vibration. Going thru the gears no stutter at 1500 rpm only when it gets to 45 at 1500rpm. Temp never gets to 210,have a new thermostat but no time to put it in yet. And the tailpipe seems really hot to me. I am thinking O2 sensor CTS or clogged cat ,muffler? any opinions would be greatly appreciated.

My 88 used to buck and stutter at almost exactly 2000 RPM at the same spot on the way to Work every morning. Something about temperature, it would get up to operating temp. at about this spot and cruising high gear at 2000 RPM and start bucking. I eventually figured out it was mostly the O2 sensor.
My low idle issue turned out to be a ground issue in the TPS, won't hurt to check the TPS ground to chassis and see how much resistance you have. I never did install another TPS ground to chassis, I just fixed what I had. It eventually turned out to be a ground splice in the harness, actually for multiple sensors.

Just an idea, when it get to 1500 RPM and starts to vibrate just touch the brake pedal, this will disengage the torque converter lockup. May tell you something, it may not.

I'll trade you your low idle for my high idle

Check the TPS voltages, engine off, and sweep it slowly from idle to WOT, but do it on the TCU, square connector side, to see if the voltage has a jump point, noisy spot, or the range is off. I think it is 17 to 87 % of input voltage from idle to WOT on the expected voltages. Also test the ECU side. Might be the TPS. If the ECU side is not calibrated it can cause low idle!