Help with diagnosing daily driver...

[andrewb70]

I am completely stumped as to what is wrong with my daily driver and I am hoping some of you might have some ideas. I have done extensive searching around on related forums and the answer seems to be as simple as IAC to recessed exhaust valves...

Vehicle: 1999 Mazda B2500 (Ford Ranger) 5 speed.
Almost 100K miles well maintained.
New plugs and wires at 75K miles.

Symptoms: Extremely rough idle when cold. This doesn't happen upon initial start up, but it starts happening after first drive and I come to a stop. From that point the engine starts to shake violently enough to make the whole truck shake. The shifter handle shakes hard and the whole truck shakes. It smooths out if I give it a little throttle, but when it comes down to idle the shaking resumes. Once it comes up to temp the idle smooths out and is mostly normal. However, when I blip the throttle and the RPM come back down, on occasion the engine will idle rough again, but will smooth out in 3-4 seconds. I can replicate this fairly consistently.

There are no codes or pending codes.

I have replaced:

IAC
Temp sensor
EGR valve
Hose from valve cover to TB
Cleaned the TB (took it off and new gasket)

Any help and ideas are appreciated.

Andrew

[Build-It-Break-It]

Have you checked fuel pressure at the rail when at idle? Also Engine off but key in on position? Also"dead head"the fuel pump into a gauge to check the pressure with key on but engine off to check pressure directly from the pump. Then again after fuel filter at the rail.

I just had my wife's fuel injected 65 mustang do the exact same thing and found low fuel pressure only at certain times. I removed the fuel pump and found split fuel line at pump and the filter had completely fell apart. Replaced line and filter and car runs like a dream again.

Keep us posted. I'll keep throwing a check list out. I wouldn't keep just throwing parts at it tho.

[andrewb70]

Have you checked fuel pressure at the rail when at idle? Also Engine off but key in on position? Also"dead head"the fuel pump into a gauge to check the pressure with key on but engine off to check pressure directly from the pump. Then again after fuel filter at the rail.

I just had my wife's fuel injected 65 mustang do the exact same thing and found low fuel pressure only at certain times. I removed the fuel pump and found split fuel line at pump and the filter had completely fell apart. Replaced line and filter and car runs like a dream again.

Keep us posted. I'll keep throwing a check list out. I wouldn't keep just throwing parts at it tho.

I have not checked the fuel pressure, but why would fuel pressure be off when cold and then "fix" itself when warm. The issue that I am having is not random. It follows a very consistent pattern that I have described.

Andrew

[Build-It-Break-It]

My wife's Mustang did the exact same thing. Ran rough at idle,warmed up and cleared up for the most part then would run rough off and on while driving like it was struggling. Below is what I pulled from her tank/ pump. I'm not saying that's your problem,just giving you ideas of what to check.

[JEFFTATE]

Andrew, Did you check the coolant temperature sensor ? Maybe it's reading incorrectly and throwing the fuel mixture off ?
Or Mass Airflow Sensor

[blitzer454]

could also be an air leak, like from a bad intake manifold gasket. When the engine warms up the gasket expands sealing the leak.

[andrewb70]

Andrew, Did you check the coolant temperature sensor ? Maybe it's reading incorrectly and throwing the fuel mixture off ?
Or Mass Airflow Sensor

I replaced the coolant temp sensor. Both of them...one for the ECU the other for the gage. Used genuine Motorcraft parts. I have not touched the MAF, but a cleaning might be in order...


Andrew

- - - Updated - - -

could also be an air leak, like from a bad intake manifold gasket. When the engine warms up the gasket expands sealing the leak.

Wouldn't this cause a high idle?

Andrew

[minendrews68]

I replaced the coolant temp sensor. Both of them...one for the ECU the other for the gage. Used genuine Motorcraft parts. I have not touched the MAF, but a cleaning might be in order...


Andrew

- - - Updated - - -




Wouldn't this cause a high idle?



Andrew

Andrew, If I'm not mistaken, the bad intake gasket could cause a high idle. I may be wrong but seems I've run across this before. Would make sense, after it heats up the leak might fix itself until the next time it cools down. Just a thought..

[blitzer454]

I had a bad intake manifold gasket in my 2003 Chevy truck. The idle ran very rough until it warmed up, so rough that to me it sounded like it was on the verge of stalling. So I would say it depends on how bad the leak is, if it's not too bad, then yes it might look like a high idle but in my case it seemed to have more of the opposite effect.

[Razzor67]

This is a common problem with this engine. Most often a bad valve or valance guide .If you can do a leak down test on all cylinders it should pinpoint it for you.
Ray

[andrewb70]

Most of these fixes are way more work that I want to do at this point...LOL...

Once it warms up, it runs perfectly.

I have read some other people suggesting recessed valves. This doesn't make any sense to me, but maybe someone can explain it. I would think that a valve problem would also include other symptoms like oil consumption etc...

Andrew

[Razzor67]

Not all the time but can and will happen when the mileage gets higher. I believe it's a Ford problem with this engine design. It's seems we do quite a few valve jobs on this model. Basically recessed valve means
The valves have worn enough along with the valve seat that the valve slides into the seat too far. So they do not seal,causing a loss of compression at lower RPM as well as loss of fuel mileage and power.
Ray

[Josh@Ridetech]

Throttle position sensor? I had one that wasn't reading the right voltage not long ago and it killed the way the car ran at idle.

[ford396]

20+ yr Ford tech here. What engine? If 4cyl likely intake valves coked badly or egr. If 4.0 more than likely upper intake gaskets which are nothing more than an oring. They get hard and will cause stall and run rough cold. Not a fast idle like you would think. Drawing in unmetered air and no fuel being added for it leads to stumble, running rough and stall when cold. When they warm up, the oring becomes more pliable and will seal better and the warmer engine can tolerate the lean mixture better. Couple things to check. If it is valves, I would try a good quality injector and top end cleaner such as BG products.

[MonzaRacer]

Also dont forget to check for vacuum leaks. Many Fords will develop small leaks in pcv system and untill it gets bigger will only effect running at certain temps, rpms, driving conditions.

[andrewb70]

20+ yr Ford tech here. What engine? If 4cyl likely intake valves coked badly or egr. If 4.0 more than likely upper intake gaskets which are nothing more than an oring. They get hard and will cause stall and run rough cold. Not a fast idle like you would think. Drawing in unmetered air and no fuel being added for it leads to stumble, running rough and stall when cold. When they warm up, the oring becomes more pliable and will seal better and the warmer engine can tolerate the lean mixture better. Couple things to check. If it is valves, I would try a good quality injector and top end cleaner such as BG products.

It is the 2.5L 4 cylinder. The EGR was replaced. I put Seafood in the gas...but I can try the BG Products...

Do you have a link to the specific product you mean?

Andrew

[andrewb70]

Just to update and get more ideas.

I have run 2 cans of BG fuel system cleaner through the system and no change.

I fiddled around with the EGR system and am pretty sure that is not the problem, because further searching around tells me that the EGR system is not working at idle. I also checked it by disconnecting the vacuum line (plugged it so no vacuum leaks) from the EGR valve. No change.

Today I finally got around to checking the fuel pressure. It was right at 64psi at idle. Using my Google Ninja skills, it seems that the factory specification in 56-72 at idle. What I thought was the FPR has a vacuum line attached to it and when I remove it (plug the vacuum leak) the pressure does not change. Further Googling around reveals that what I think is the FPR is actually a fuel system damper. What's throwing me is that it has a fuel return line hooked to it...so not sure what to think there.

Yesterday I also had it at the Mazda dealership. All they managed to do was break the EGR tube with nothing improved. The Ford dealership in town won't touch it, although they are probably the best people to look at it.

I also turned the throttle blade screw 1/8 of a turn. This drove the idle speed up a little and set a P1506 code. Frankly I rather have a hanging high idle vs. having stalling issues, so I am leaving it like that for now. I also cleaned the MAF sensor, although it looked pristine.

I was also thinking that it might be PCV related. I essentially rendered the system inoperable (plugged all vacuum hoses) and it made zero difference. Cleaned the PCV valve (it looked fine) and put all the hoses back on...again, zero change.

Super frustrated!!! Need help.

Andrew

[andrewb70]

This is a common problem with this engine. Most often a bad valve or valance guide .If you can do a leak down test on all cylinders it should pinpoint it for you.
Ray

Ray,

I have a really hard time believing this is the problem, because this engine has been around for decades and by all accounts, recessed valves don't seem to be a systemic issue. But who knows...

Andrew

[Kenova]

Time for a LS swap.
Yeah, I know, not very constructive.

Ken

[TheJDMan]

It is the 2.5L 4 cylinder. The EGR was replaced. I put Seafood in the gas...but I can try the BG Products...
Andrew

You put "Seafood" in the gas? Hmm, I learn something new everyday!