Rough idle cold.

[osteologation]

Been doing a lot of searching and reading.
Can't seem to find a duplicate to my problems.
Firstly when cold and you start it, it jumps to 1500 rpm then almost immediately drops to 800 or so and runs rough. The initial take off is a bit abrupt with gear changes ( it is a 5 speed ). Once warmed it's great.

Cleaned iac
New tps
New fuel pump
New plug/wires/air/fuel filters
Cleaned maf
New plenum gaskets
I capped the vac line to egr as the tube is missing

Now tonight after replacing plenum gaskets it still ran rough
I unplugged maf it stalled. I restarted truck and had to give it some throttle but eventually it evened out and ran really smooth. Idled great even. Haven't ran codes lately but last time around I got an egr error and a lean code. Also when smooth vac is great but when rough it is fluctuating a good bit. I assume from missing. My o2 sensors look ancient. Prolly old and in need of replacement. But it does get reasonable hwy mileage. I avg about19-19.5 hwy 15 around town.

It's frustrating as it's only when it cold.
Now I checked the ect warm with a multimeter ( can't find the page with the numbers again tho) and it was fine. Is the fact that the rpm drops so quick at startup odd? Shouldn't the rpm stay up for longer?

 

[something9000]

i would start by replacing that tube and then the o2 sensors. Since the engine runs a little rich until its at operating temp when its cold they might be sending some crazy voltages to the ecm

 

[osteologation]

i would start by replacing that tube and then the o2 sensors. Since the engine runs a little rich until its at operating temp when its cold they might be sending some crazy voltages to the ecm

I thought about that. Egr function is only at operating temp at part throttle. I capped because it was whistling when the egr opened driving through town lol. And I was under the impression that the computer didn't use the o2 until warmed up either. I could be wrong. I was reading through the fordfuelinjection.com explanation of how the system works from engine start through the various modes.

I wanna do an engine swap in the next 3 or 4 months so I wanna keep replacements to stuff I can use later. Replacing an o2 of unknown age or egr components is never a bad idea. I'm also going to tinker with mass air possibility and try to tighten lower intake down.

The main thing is that it didn't always do this. And the fact that's only when cold strikes me as a mechanical issue. But even tho I'm not in an emissions testing state I would like to keep egr, etc working even if for easier troubleshooting.

 

[1AJeremyD]

Is it possible that you have a air leak someplace? Does it sound like your sucking in air anywhere? It could also be related to an injector being slightly clogged

 

[osteologation]

Is it possible that you have a air leak someplace? Does it sound like your sucking in air anywhere? It could also be related to an injector being slightly clogged

I thought about the injectors as I've had to replace them on vehicles with less miles. The fact that vacuum is 20" ad soon as you start it and only fluctuates when the idle fluctuates.
When started it runs smooth but just fir a few seconds maybe 5 or 10. The as the idle settles down it will pick up a what seems like a miss but then smooth out ad it warms up. I pulled all the plug wires one at a time and each one made it worse so I don't think it's actually missing. Maybe a sticky or poor performing injector?

After the the mass air clean and plenum gaskets, it is marginally better. I should reset computer and run codes, it's a bit of a chore tho lol since my CEL is burnt out.

 

[osteologation]

I unplugged my new tps and it idles fast till warm and smooth. New tps bad? Prolly.

 

[osteologation]

Well i verify'd the tps with the values of fordfuelinjection.com and my tps is within spec.
It runs great with it unplugged, less so plugged in. Does anyone think that the values are not matching between the mass air/tps? according to my mutlimeter i get .94v at idle and 4.62v at WOT. But why does it run better when tps unplugged?

 

[osteologation]

Well as update I have replaced O2, pcv, lower intake gasket, valve cover gaskets, orings, coil pack, and injectors. Injectors and coil pack are low mile used units, and with 203k miles I figure it's not unrealistic to change them.

Well after 6 hours roughly of cleaning and replacing parts I fired it up and it ran....about the same. A bit smoother maybe. So I look and look and find that my egr is sucking air. Used the old intake gasket to make a block off plate and the truck runs butter smooth. I will eventually replace the entire egr system bur for it works.

It was not all for naught though, my intake gasket was nasty and valve covers were leaking pretty good. And I have a cyl that the plug looked slightly lean on so I hope these injectors help with that. The threads had a darker blue tint and it had very little of the white/tan coloration compared to my other cylinders.

Motor was super clean inside. Idk if it's original but it's impressive for over 200k.
Easy if not time consuming. A parts washer would have been nice as it was very dirty on the outside of engine.