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James, Ford Technician
Category: Ford
Satisfied Customers: 3628
Experience:  Ford Senior Master Tech, Ford gas and diesel expert, ASE Certified
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I have a 99 7.3l powerstroke that has been having a problem.

Customer Question

Hello, I have a 99 7.3l powerstroke that has been having a problem. When it is cold, it idles extremely rough and doesn't respond well to throttle at all. However, if I leave it he block heater plugged in overnight, it has zero issues at all. Ambient air temps have been between mid 70-90's, so it's not like I should need to keep the block heater plugged in, but this is what we have had to do the last couple months. Could this be a waste gate issue?
JA: Is the rough idle intermittent or consistent?
Customer: Consistent when cold
JA: What is the make/model of your car?
Customer: 99.5 f350
JA: Are you fixing your F350 yourself? What have you tried so far?
Customer: I will most likely be doing it myself once I get home in a few weeks, so i am research now. I have not done much else so far as I am offshore and am only hearing what my wife has informed me of
JA: Anything else you want the mechanic to know before I connect you?
Customer: No
Submitted: 8 months ago.
Category: Ford
Expert:  James replied 8 months ago.

Hello, do you have a test light or volt meter to do some testing. if you have a weak glow plug relay or glow plugs you can have this concern. It sound like it is the issue since it doesn't do it if you plug in the vehicle.

Customer: replied 8 months ago.
I do have a voltmeter as well as a test light, and the plugs themselves are all new as of a couple months ago, although I have not tested the relay. How would I determine if the relay itself is weak?Would this cause rough idling and running for upwards of 15 minutes?
Customer: replied 8 months ago.
Also, when I turn the key to On, I have an LED that I installed showing the relay is on as well as I can view the drop in battery voltage on the in dash gauge until the relay kicks back off, which depending on the day can be 30 sec to 2 minutes.Regardless, I have heard of this issue causing hard starts, but never idle issues for such long periods. But I'm not the mechanic and am here asking you. Can a Glow Plug Relay cause rough idling and lack of throttle response for long periods, like 15 minute long periods until the engine is warm? If not, what could (besides needing to rebuild/replace injectors or HIPOP)
Expert:  James replied 8 months ago.

You want to test the glow plug relay for internal resistance not the voltage drop the battery has. if the glow plug relay has more than .3v voltage drop it will cause hard starting and rough running until it warms up. If that is ok then you could have injector o rings that need to be replaced.