Rough Start - For About 30 Seconds

[joefnh]

I have a 2003 Explorer 4.0L XLT 4WD with 301,000 miles.

Has a rough starting process that the RPM’s jump up to maybe 1500 and then dip and sometimes stall, it does this RPM cycling a few times but after about 30 seconds, it idles fine and will be fine throughout the day as long as the engine is modestly warmed up. The confusing part is that there is a real time limit for this behavior of about 30 seconds and then runs and drives fine. First thing in the morning the engine will not have warmed up in 30 seconds from a cold start, but this time issue is repeatable each time. I can drive to the store and be there for an hour come out and it starts and idles fine. If the car sits overnight it will start rough again and after this roughly 30 seconds then runs and drives fine

So here’s a list of what I know and have done:

- No codes displayed or are pending, checked several times
- I have cleaned the MAF sensor 2 times including the connectors with MAF cleaner
- Replaced the IAC
- Re-seated all plug and coil wires.
- I have used the old starting fluid check to see if there are any vacuum leaks. Sprayed around the intake manifold base and the throttle body. I have not measured the vacuum level yet. With the very real time factor Involved where the problem goes away with either time or being warmed up, it doesn’t sound like a chronic vacuum leak issue

With the issue of the engine being slightly warmed up and the short time where the problem stops, this seems like some type of sensor issue and the computer causing the rough start. This is a very high mileage vehicle but it runs great, does not burn a drop of oil and still gets about 18 - 19 MPG (mixed driving) The engine has no knocks or ticks. I have meticulously maintained the vehidle.

Any ideas??


Thanks

-Joe

 

[AA7KN]

I have a 2003 Explorer 4.0L XLT 4WD with 301,000 miles.

Has a rough starting process that the RPM’s jump up to maybe 1500 and then dip and sometimes stall, it does this RPM cycling a few times but after about 30 seconds, it idles fine and will be fine throughout the day as long as the engine is modestly warmed up. The confusing part is that there is a real time limit for this behavior of about 30 seconds and then runs and drives fine. First thing in the morning the engine will not have warmed up in 30 seconds from a cold start, but this time issue is repeatable each time. I can drive to the store and be there for an hour come out and it starts and idles fine. If the car sits overnight it will start rough again and after this roughly 30 seconds then runs and drives fine

So here’s a list of what I know and have done:

- No codes displayed or are pending, checked several times
- I have cleaned the MAF sensor 2 times including the connectors with MAF cleaner
- Replaced the IAC
- Re-seated all plug and coil wires.
- I have used the old starting fluid check to see if there are any vacuum leaks. Sprayed around the intake manifold base and the throttle body. I have not measured the vacuum level yet. With the very real time factor Involved where the problem goes away with either time or being warmed up, it doesn’t sound like a chronic vacuum leak issue

With the issue of the engine being slightly warmed up and the short time where the problem stops, this seems like some type of sensor issue and the computer causing the rough start. This is a very high mileage vehicle but it runs great, does not burn a drop of oil and still gets about 18 - 19 MPG (mixed driving) The engine has no knocks or ticks. I have meticulously maintained the vehidle.

Any ideas??


Thanks

-Joe

well Joe, have you reset your computer ? you should remove the electrical connector from the IAC with the motor running ( warmed up) and it should idle at 500rpm. if it does not, remove the cover from the front of the throttle body, look there on the front, you should find a threaded rod that you can turn to adjust the idle. there is no slot or head on it, i used needle nosed pliers. adjust it for 500 rpm than connect the electrical connector, the rpm will surge then settle down at about 8 to 900 rpm. that is correct. now turn off the engine and disconnect the battery cables from the battery and touch them together for about 30 seconds or so, this will drain the memory from the ECU, so connect it up again, start the motor and go driving, the computer will learn all over again and hopefully learn the idle and new everything. it sounded like the computer didn't know how to control the engine when it was in "closed loop" meaning not warmed up...and after it warmed up, it switched to open loop where the computer was controling everything. so try making sure the idle is correct, and reset the computer and let us know what the outcome is...good luck

Mike

 

[TechGuru]

When was the last time you replaced the spark plugs?

Mine turned out to be the cause when I had a similar problem.

If you're using anything other than Motorcraft SP500 replace them anyway.

 

[J_C]

I'd guess your spark plugs are worn in combination with the battery being weak (or a parasitic drain on it) so it takes a few seconds to get the voltage up higher for better spark. Could be other things but this is easy enough to check, put a charger on the battery and try to start it after topped off... might not be perfect running if plugs are bad but should improve markedly.

The more generic answer is hook up a scan tool capable of live data and see what's shown. Along with everything else I'd look at long term fuel trim and the coolant and any other temp sensor.

 

[LMHmedchem]

If you're using anything other than Motorcraft SP500 replace them anyway.

I have used Bosch double iridium on all of my vehicles for a while now. What is the reason to use the Motorcraft platinum (other than that they are half the cost)?

I really like the little cardboard gap protection tube on the Bosch. Though I always check, I have never had to adjust the gap on one of these. Simple but good idea.

I have never tried ruthenium but I probably will next go around.

LMHmedchem