Rough idle

[03MERCMARAUDER]

So before the Nazis jump in I have done the searches and spent a good amount of time reading the different issues and fixes people have done. I recently purchased an 04 marauder off the boards here and it had a rough idle which bugs me. I love the car and do not regret the purchase at all but I have had one of these cars when they were new and it had a smooth idle even after a tune. Car I purchased has the a Lidio tune, older JLT CAI and 4.10 gear. When I first got the car I noticed it would surge when I left off the brake at a light. I was able to fix this by upping the idle RPM in drive but that has its draw backs. I even swapped the stock tune back into the car and still had the same issue.To date I have replace the plugs (proper gap) New OEM coils, motor craft Fuel filter, I cleaned the IAC as well and the MAF and still fight this idle issue. I can hear it through the exhaust even at idle. So what am I missing? Any words of wisdom from the veteran folks on this board? Appreciate any help

Joe

[BlackBeauty_bb]

have you checked for any vacuum leaks?

[musclemerc]

EGR valve is stuck open. Big ole vacuum leak

[crownvic97]

When I bought my Marauder it had a rough idle as well. Replacing the plugs made no difference. A compression test showed low compression on cylinder 8. I’d suggest you do a test as well.

[TooManyFords]

As already suggested, either the EGR or your IAC. Just cleaning the IAC does not mean it will work correctly. Also, make sure you get the Ford one and not an off-brand.

Surging is excess air, so you also might want to get a can of starting ether and spray around the various hoses connected to the intake, and also around the intake runners by the heads as well. I bought a Marauder to put back together and it had a rough idle. Turned out the lower intake by #1 was cracked and it was afterwards I found out it also had a nitrous kit on it at some time. I found it with the Ether trick. I'm guessing it was not setup correctly and backfired which cracked the intake.

What you describe is most likely an easy fix. Keep looking and you'll find it.

[blazen71]

When you spray the ether, the rpm's will increase if there is a vacuum leak cause the engine is sucking it in and burning it.

[Marauderjack]

If you need a Brand New IAC Valve I have two made by Hitachi who made 'em for Ford according to Bob!!;)

PM me if interested!!:beer:

[03MERCMARAUDER]

Thanks for the suggestions I will give it a try today

[fastblackmerc]

As already suggested, either the EGR or your IAC. Just cleaning the IAC does not mean it will work correctly. Also, make sure you get the Ford one and not an off-brand.

Surging is excess air, so you also might want to get a can of starting ether and spray around the various hoses connected to the intake, and also around the intake runners by the heads as well. I bought a Marauder to put back together and it had a rough idle. Turned out the lower intake by #1 was cracked and it was afterwards I found out it also had a nitrous kit on it at some time. I found it with the Ether trick. I'm guessing it was not setup correctly and backfired which cracked the intake.

What you describe is most likely an easy fix. Keep looking and you'll find it.


When you spray the ether, the rpm's will increase if there is a vacuum leak cause the engine is sucking it in and burning it.


If you need a Brand New IAC Valve I have two made by Hitachi who made 'em for Ford according to Bob!!;)

PM me if interested!!:beer:

What ^^^^^^ they all said!

[03MERCMARAUDER]

No vac leaks found using ether so guess I will look at replacing the egr and iac to see if that resolves the issue. Will also do a compression test this weekend. Other than the idle the car runs fine. Its just enough that you can see a shake to the motor and feel the car shake

[crownvic97]

No vac leaks found using ether so guess I will look at replacing the egr and iac to see if that resolves the issue. Will also do a compression test this weekend. Other than the idle the car runs fine. Its just enough that you can see a shake to the motor and feel the car shake

I wouldn't bother replacing any parts before doing the compression check. Its quick and easy and may save you from throwing parts at the problem.

[03MERCMARAUDER]

Update. I tossed a known good egr valve on and no change to the rough idle. Plan is to do a compression check tomorrow. I put my x cal on the car and this time I had codes. Had code P0316 and code for cylinder 8 misfire. I swapped cylinder 1 COP with cylinder 8 and cleared the code. Fired the car up and still has rough idle and after a short drive same codes are back so cylinder 8 is where I will focus. Based on the research I have been doing I am afraid I will find low compression on cylinder 8 but I may be wrong. Stay tuned.

Joe

[crownvic97]

Update. I tossed a known good egr valve on and no change to the rough idle. Plan is to do a compression check tomorrow. I put my x cal on the car and this time I had codes. Had code P0316 and code for cylinder 8 misfire. I swapped cylinder 1 COP with cylinder 8 and cleared the code. Fired the car up and still has rough idle and after a short drive same codes are back so cylinder 8 is where I will focus. Based on the research I have been doing I am afraid I will find low compression on cylinder 8 but I may be wrong. Stay tuned.

Joe

This is the exact same symptoms and outcome I had on mine. Misfire on 8 that stayed on 8 no matter what was changed. I’ll be hoping that you have a better outcome than me!

[03MERCMARAUDER]

This is the exact same symptoms and outcome I had on mine. Misfire on 8 that stayed on 8 no matter what was changed. I’ll be hoping that you have a better outcome than me!

Head have to come off your car?

[crownvic97]

Head have to come off your car?

Yes, I took it as an opportunity to upgrade however. You could pull just the driver side head and have the valve/valve seat repaired on 8 (assuming That’s the issue which is likely).

I bought some 9 thread heads, had a valve job and some porting done to them, and basically replaced everything other than the shortblock. Still not done!

[03MERCMARAUDER]

Yes, I took it as an opportunity to upgrade however. You could pull just the driver side head and have the valve/valve seat repaired on 8 (assuming That’s the issue which is likely).

I bought some 9 thread heads, had a valve job and some porting done to them, and basically replaced everything other than the shortblock. Still not done!

Yeah I'm afraid this could snow ball into a big project lol

[Bondfreak13]

My 2003 Had a Ruff Idle. After Changing the plugs and Coils, Which were the Factory originals from 2003 BTW, There was no change. Got a Compression Test and it was #8.

[03MERCMARAUDER]

Ran compression test today. Test was done with engine cold and each cylinder was cranked same amount of times. Sadly have an issue on #8. Numbers were

#1-220
#2-225
#3-215
#4-225
#5-200
#6-205
#7-185
#8-85

[Zack]

The valve seat dropped.

[Turbov6Bryan]

Dont buy other heads, get yours freshened and have them install 8 time zert fittings to get the same advantage the 9 thread heads have.

8 time zerts installed is wayyyy cheaper than buying some other heads.

Other than the labor involved, this is a common repair.

Good luck!