Persisting High Idle / bucking

[seth959ci]

My 89 has been giving me fits for about 2 months now as it idles high, throttle is very slow to drop off(i.e. blipping it at idle or between shifts), and in higher gears the truck will intermittently buck/shutter under medium throttle loads. when this occurs it feels like there is a lack of power as well.
i have changed the following parts
-ECM
-IAC
-TPS
-o2 sensor
-EVR
-spark plugs/wires
-DIS module(has been relocated due to broken bolt in factory mounting holes)
-Also no engine Codes
I have not noticed any vacuum leaks.
Any ideas? Kind of at a loss right now. had it at a shop for 2 weeks and they couldn't figure it out either

 

[seth959ci]

any ideas? vacuum leak?

 

[97ranger xlt]

pcv valve?

 

[seth959ci]

ill check that out, thanks!

 

[warment]

Replace the DPFE sensor. My 2000 GT mustang did the same thing...hanging idle...the sensor is a little black box on the firewall...it is part of the EGR system.

 

[Earl43P]

I'd test the Fuel Pressure Regulator.

http://oldfuelinjection.com/?p=41

 

[seth959ci]

replaced the dpfe, also did not notice any fuel coming out of the FPR but i may pick up a guage and test the pressure. thanks for the input

 

[scotts90ranger]

have you checked for a proper idle speed without the IAC connected? it should be about 500rpm without it connected.

An '89 doesn't have a DPFE, it has a EGR position sensor, if the EGR was bad it should cause a low idle most likely unless the diaphragm is bad.

I would start by checking the idle, then unplug the vacuum lines one at a time (skip the brake booster and MAP sensors, those would be less likely than the hard lines.

 

[seth959ci]

my egr is currently blocked off, has been for about a month... would that cause an issue? i did it in hopes that it would temporarily eliminate the egr from the list of possible problems with the truck(was throwing a code 31 before hand).

i also just checked the fuel pressure. With the key on it was about 40 psi and then it dropped to 30 psi over the course of 90 seconds. Pressure was about 30 psi when running.

another thing i noticed is that while idling, i revved the engine up to about 2200rpms and held my foot steady. The rpms would fluctuate +- 150 rpms.

i do not know much about fuel pressure yet and if it may be causing these issues, so any help or input is greatly appreciated!

ps. FPR does not appear to be leaking fuel into the vacuum line.

 

[seth959ci]

should the fuel pressure drop like that?