Hard start and rough idle ideas...
 

I have an 89 F350 w/460 efi.

I have been running into a few annoying issues. First the trucks idle has always been unsteady since I bought it, about 500 miles ago. Also it is a little hard to start when its hot/warm.

First thing in the morning or after it has sat for a few hours it start right up with maybe 1 second of cranking. Once warm it takes maybe 3-4 second of cranking and it barely starts up. It will catch and stumble and stutter at about 3-500rpms for a few second and then it will idle OK. It always starts, never stalls and runs pretty darn well.

This is what I have done so far:

distributor cap
rotor
motorcraft copper plugs
wires
fuel filter
new rear fuel pump assembly
all new fluid in everything
new rad. hoses and thermostat
oil pressure sending unit
coolant sending unit (gauge)
coolant temp sensor
intake air temp sensor
idle air control valve
set timing to 13 degrees with spout unplugged
*updated list of parts*

I think I may back the timing off a little to see if it helps the hot start issue. I am going to install the coolant temp sensor for the computer, then if that does nothing I will replace the TPS. After that I guess the ambient air temp sensor if it has one.

Anyone have any other ideas and or disagree with my thoughts? I am also going to get those rubber plug wire holders so the plug wires are not laying on top of each other.

Have you got any codes from it? I mean an ECT is cheap enough and can't hurt, I just hate for someone to just throw parts at it.

What is an ECT what does that stand for?

Engine Coolant Temperature unit, what you are referring to as a sending unit. Sending unit is the terminology when referring the the gauge sensor, and sensor when referring to the computer one. Like I say, cheap enough and can't hurt, but why not see what codes you get first?

Fuel Injection Technical Library » Engine Coolant Temperature Sensor (ECT)

Item C176 in this photo
http://repairguide.autozone.com/znet...3f80225096.gif

Warm up the engine then do this: Fuel Injection Technical Library » How To Run a Self-Test

or purchase one of these: Equus 3145

I replaced the ECT today. So both the coolant temp sender and the coolant temp sensor have been changed. I ordered the IAC sensor and the ambient air temp sensor and they will be in tomorrow morning.

The idle seems to be a little smoother since I put the coolant temp sensor but its still not 100% right. And its still hard to start when hot. So hopefully the two things I order fix the problem. If not I am going to set the timing back to 10 and work my way up slower.

Try running a tank of Techron by Chevron through it. Over time the valves get a build up and on cold start actually fuel will build and "drip" off the valve causing stumbling and rough idle. Seen it many times and a cheep fix.

Ordered the code the reader and I also replaced the idle air control valve and . Seems to idle much smoother, but it now likes to idle at 1000-1100 rpms unless I load the motor a little and it drops down to like 700-800 but a little rough. Anytime I am drive and push in the clutch it will idle smooth as can be at 1000ish rpms.

At first start up it will idle a little lower like 800-900 and with a slight hiccup or roughness.

I am going to check the codes Saturday and re time it tomorrow.

Well as much as I hate to just throw a bunch of parts at a vehicle becasue its not running correctly, every sensor and sender I have fixed seems to help/solve parts of the problem.

I have to assume that a truck that is 22 years old with only 46,000 miles did a whole lot of sitting, probably for a few years at a time at least over the past few years. I believe many of the senders and sensor are failing for some reason. Oil pressure sender and coolant temp sender both didn't work. The air charge sender definitely made a difference in hot start and the idle air control valve smoothed out the idle.

So i figure its probably worth while to change the MAP sensor and the oxygen sensor also. I figure any sensor/sender that affects the air/fuel ratio needs to be check and or replaced.

Only things left I can think of are the TPS, some fuel pressure sensors and the egr stuff. But I think those are ok. Although the TPS could affect idle and starting.

Anyone know why my idle went from rough and stumbling and then after may changed parts is smooth but high @ 1100rpm only after its warmed up. When cold it idles @600-700 and little rough.

Also when you first start the truck cold or warm and the idle is low and stumbling the truck gets a very small amount of what appears to be excesses fuel smoke at idle. If you hold the throttle at 1000+ rpms it no longer smokes and once it warms up and the idle sets to 1100 there is zero smoke.

I think this is either fuel pressure related (too much pressure at idle) and or TPS. Maybe the TPS is not seeing the correct throttle opening or lack of opening and is causing the high idle. Could the EGR be causing higher than normal idle?

Many of the aftermarket suppliers have less than desirable quality control. You could have introduced a new problem with all the new parts. Did you check for codes yet?

yeah the only code I got was 85. Which I guess has to do with the fuel tank venting in that canister on the passenger side up by the radiator. Could this cause any idling issues, I assume not considering its just a vent. it appears that there is a small hose missing on the top canister and a larger one missing on the bottom canister. I have no idea there they come from and what they are for. I suppose I should try and figure that out...

Time to start pulling out the new sensors one at a time to see which one may be causing your new issue. As a test remove the IAC connector, does the idle drop back down? If so, start checking those new sensors you installed. You could have invested in a DVM and tested those sensors before you blindly replaced them.

Code 85 typically will not cause a high idle. The Canister Vapor Purge (CANP) solenoid is used to release fuel vapors into the intake when the PCM commands it to open. Item C171 in the drawing I posted earlier.

I saw in your other thread about the Code 85 problem you are concerned some pieces are missing. I think you are mistaking the AIR injection components for the fuel vapor canister.

A photo of what you are seeing would help everyone out with diagnosing this problem. You can also refer to the line drawing I posted earlier.