Already check and readjusted my tps, o2 sensor is very new with only 350 miles on the new one and I do have an exhaust leak because the gasket between my down pipe and cat is shot but that's to far from the o2 sensor to do anything. When I got her, her header was almost completely shot, but I was able to weld it up but maybe one of my welds cracked. I wanna replace it anyways. Does anyone have the exhaust manifold/header to a renix 4.0? Idk if the h.o. 4.0 has the same header but if so I'm looking for one in the sub $100 range cuz I'm broke. Please help!

 

No they are slightly different, but some guys make them work with a little massage here and there, also the down pipe would have to be changed cuz its a different angle off the header...

 

I had what sounds like the same symptoms, down to the extra bad mileage with (703's) here. It's pretty easy to at least check the (large red), 02 sensor heater wire. My 02 heater power was fine, but the sensor itself tested crap. Even with a cheap analogue meter, the new one tested right on and works great! (went from about 11, to about 16, putting around.) Also the engine temp comes up twice as fast, and the idle smoothed out.

That 02 heater power has it's own relay btw.

 

Later headers have no 02 sensor bung, no EGR bung, and require a different/modified headpipe.

 

Ok so that's a no go on the h.o. Header but imma test my o2 heater right now

 

Well?

 

Well it works but my idle smooths out when warm so idk

 

I have the exact same issue as you. The idle fluctuates up then comes back down amd almost stalls, then normal for several seconds. Then the whole process over again till warm. My MPG is crap and I overheat now. I fail emissions with C02 at 150 and 20 acceptable.

What I've done so far:
Replaced all vacuum lines and fittings
Replaced map sensor
Replaced 02 sensor
Replaced TPS sensor
Replaced ECU
Checked exaust leaks
Cleaned and seafoamed TB and intake
Tested fuel rail pressure
checked all injectors
Replaced fuel pump and filter
.........and I think I covered it all with little to no improvement.

 

Cap, rotor, plugs, wires?

 

Yes, all with less than 500 miles.

 

Tps adjusted?

 

I've done pretty much everything he has with no improvement. My mpg is 16 when it used to be 20-22 now it runs around 210 degrees when normally my running temp is 180 ( have a 180 thermostat in there) and no that isn't the problem cuz it's been like that since ive owned it. I have no idea what the problem is.

 

Just did it again today. I disconected the battery and touched the cables to drain the electrical system to see if reseting the ECU would help. No change.

 

That doesn't work on a Renix.

Have either of you refreshed your grounds and done a sensor ground check?

 

Figured it was worth a shot. I have not refreshed my grounds. I will try that tomorrow.

How about the intake air temp sensor? The two wire sensor that is in the intake manifold behind tje TB. Could that cause me to be running so rich?