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Shakey idle

1995 f150 5.8 263k

My truck shakes at idle and it worsens the longer I am sitting there. Symptoms are in park or drive and any engine temperature. KOEO/KOER: 111

Sensor tests with engine at temp:
Elect pressure Ctrl: 5psi/9.88V
Engine coolant temp:181F/0.71V
Pulse width 1&2: 4.22/4.3ms
HO2S 1&2: rich&0.54V/rich&0.22V
IAC: 32%
Intake Air T: 87F/2.61V
Loop status: closed
MAF: 0.88V
RPM: 688
Spark advance: 16deg
Short term FT bank 1: 4%
Throttle position mode: CT
Throttle position: 0.97V
Vehicle power: 14.06V
V Ref: 5V
KOEO Fuel P: 38psi
KOER Fuel P: 31psi
FPR: no fuel and +10psi
Manifold vacuum: 20psi

Parts replaced/work: distributor, wires, plugs, ignition coil, DPFE sensor, IAC, rattled PCV, confirmed EGR valve not stuck, cleaned MAF, air filter, vacuum leak check with carb cleaner, confirmed ticking on 6 reachable fuel injectors, fuel injector cleaner.

I’m running out of ideas here guys…


Micro Machine Manager
This sounds a lot like my truck.

I'm a 300-6 though. The MAF (MAP for me) was a big deal. EGR Solenoid and cleaning helped. My fuel tank selector eventually had issues to and got replaced, but it was from a bad ground that kept blowing everything out. Same with 2 or 3 TPSs going bad (because a ground kept working through the wiring and causing resistance/hard voltage pulls to blow out components much faster than advertised).

There were two ground issues. The first was just an improper ground engine to battery engine to frame stuff. So as long as the battery to frame and engine to frame (if I'm getting this right?) then that takes care of that, but someone had done engine to battery directly and caused grounding and voltage issues, blowing out components non-stop over a few years.

Second ground issue was actually in the transmission itself. There's a pig-tail transmission control cable (I might have the name wrong). This continued to blow my MAP Sensor (like, 7x in 10K miles). Once that repair was done I've made it 10K miles on one MAP Sensor before it blew again (I suspect there is some corrosion again in the wiring at the transmission, an imperfect repair).

EDIT: Just checked since I was on Rock Auto and confirmed with Google. Yeah, it's called the Automatic Transmission Kickdown Solenoid Switch which had a pin completely rotted out of it. It's in the Transmission Pan from what I understand. The Pigtail it connects into can also become corroded. It handles shifting, so rough idle could be indicative of searching for the transmission position and not knowing to kickdown or not. Common tongue for this is apparently "Shift Solenoid."

Grounds causing voltage issues causing rough idle is what I suspect based on my own experience with my truck doing this for a few years before we ironed it out.
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Thanks Kaajot! Dusty had me measure some Volts before also, but nothing seemed abnormal.

With nothing else making sense, I cleaned the throttle body. I definitely ignored that “do not clean” sticker, but I did use throttle body cleaner for coated throttle plates. FIXED!!!

There is still a slight shake (10% of what it was before maybe), but judging by how the intake looked, that needs to be cleaned as well.

Anyone know a good way/place to clean the intakes? Mine is COVERED in sludge, I think it needs to be soaked. Also, what else should I look at doing while I’m in there? I’m thinking fuel injectors and redoing the vacuum lines, maybe I’ll even route them on top for easier access like dusty had in one of his pics.


Micro Machine Manager
In my similar experience, we did rebuild vacuum lines. Very easy, worth it, used some tape to color code the ends (red, blue, green etc) so easier to trace. I kept the running the same as long as it didn't look like the lines were against anything suspect to cause excessive vibration wear or worse, lots of heat wear.

I have an After Market Throttle Body that the fellas on here were like, "Big Mistake" a few years ago. I think they're right and I'm looking to get an OEM to re-install over the Throttle Body. I have a washable K&N Filter that replaced the stock atm, may go back to the OEM and just buy new filters, which leads me to the point: If yours is cleanable, probably carb cleaner/dawn rinse repeat til the black/grey water is gone and then let dry with a fan or air blowing good outside (without the filter blowing away). If it's not a washable, buy a replacement filter?

Fuel Injectors were near the end of my "last ditch" efforts on my older engine. It can't hurt to get new ones if you're bored and want to give yourself a baseline of X-Miles before a serious overhaul. My previous experience is make sure your gaskets are done right, else you'll just have problems after a nice job putting new injectors in only to have to redo your gasket. I can't speak to best practices -- think I've tried multiple methods and have little insight on it other than FML - Again?!?

Oh, just thought about this: Have you adjusted your throttle body pin to meet RPMs after start-up at idle? That's always a good place to check for anything slightly out of spec on your engine's idle (and you've probably backprobed the TPS?) After cleaning out that air filter (and maybe rebuilding the vacuum lines), calibrate that throttle pin if it still feels a little searching/jumpy at idle. Make sure TPS is good too of course.
I did plot the TPS with my scanner and it looked good. Where/what is the throttle pin? I was only aware of the non-variable TPS sensor and the idle screw that everyone usually says not to mess with. Is there something else?


don't play well w others
No throttle pin on your or his truck. He is talking from YouTube.
At least he tried to help you
I Thank him for that. No one else does

Your new symptoms I answered. Sorry.