98 3.8 5spd will not idle and runs rough

I have a 98 V6 5 speed Mustang with 200K. It will not idle and when you force it to run it runs very rough. I put a new IAC on it with no change. It loses fuel pressure as soon as it is shut off. Since it seemed to be a fuel supply problem, I put a new fuel pump on it. I replaced only the pump, using the old basket. No change. I was told by one mechanic that the cats were probably plugged so I disconnected the exhaust at the header. No change. I put new spark plugs in, new fuel filter, new air filter, new PVC, new vacuum hoses, new O2 sensors and cleaned the MAF sensor. No change. Did compression test on all cylinders and they all checked out ok. I then removed the upper intake manifold and removed the injectors. Injectors were not professionally tested but I cleaned them using the “carb-cleaner pressurization and 9v activation method” and they all put out a spray pattern. Reinstalled with all new O rings. The fuel regulator shows no signs of leaking gasoline, so I assume that it is not the problem. I have to admit that I am totally stumped. Is there anyone out there that might direct me on what to do next? Could it possibly be ignition instead of fuel? I thank anyone who can help me with this problem. Thanks.
 
Just finished testing the resistance of the coil pack. The primary resistance was 1.3 Ohms on all three coils. Chiltons says they should be below 1.0 Ohms. Secondary resistance was also out of spec. All three measured at 13,000 Ohms with spec at 11,500 max. I think I have found my problem.
 

BRN2RUN

Active Member
I don't think it would be an EGR problem....I've never had an EGR problem, but the worst that could happen (as far as I know) would be that you'd get a check engine light, like the guys that intentionally remove their EGR.

Before you do anything else and buy more things that don't find the problem, check your car for vacuum leaks. Vacuum leaks make a car run very rough (rough idle, stalling, etc). Check all your hose connections going to or from the upper intake manifold. For example, after taking off my upper manifold and putting it back on, I forgot to hook up the hose below the throttle body (right below the IAC) and the car ran like absolute crap. Whoops! Get your system pressure tested or smoke tested, but if you don't want to spend the money, buy a couple of feet of hose from your local hardware store, and get an old spray bottle (or buy one) and put some soapy water in it and spray all the hose connections and hoses (pinhole leaks can occur), as well as your IAC and throttle body gasket area where it connects to the intake manifold, and the PCV entry/ return (as these can sometimes leak). Connect your hose to one of the ones that run off of the intake manifold. Then, blow through the hose and see if there's any bubbles or air coming out of any of the hoses or connections. A good set of lungs will find a vacuum leak--I've done this on both of my cars with success. You'll hear a bit of leakage at the throttle body, and this is normal. Everything else should hold under pressure:

There may be one or two that I forgot, but those are all places to start. Also, if there's any leak at your throttle body gasket or IAC gasket, that would cause a vacuum leak.

There's a possibility that your O2 sensors could be bad, as well, but do the vacuum leak test first.
 
Thank you Brn2run. I have no egr codes but I think they only get set if no egr flow is detected. If egr is stuck open, it acts as a vacuum leak. I have replaced most of the vacuum lines with new tubing. I don't recall a vacuum connection below the throttle body. Are you sure a 98 v6 has a connection there? I will recheck that. O2 sensors are new. Throttle body gasket is new. PCV grommet is new. EGR valve should be here in a day or so. I will post the results. Again thanks.
 

BRN2RUN

Active Member
I don't have a '98, but I know that on the '99's, at least, there is a vacuum hose going to the area under the throttle body, at least. Any hose that runs off of the upper manifold should be checked.
 
New EGR valve did not solve the problem. I have checked the vacuum lines and cannot find any leaks. Could a malfunctioning DPFE cause my symptoms? Thanks
 

BRN2RUN

Active Member
Sorry to hear that you're having this many problems. Get a fuel pressure check--it should be about 39-40 psi.
 
I should update this thread as it might help someone who is chasing P0171 and P0174 lean codes. The one vacuum line that I failed to check and that turned out to be a culprit was the hose running from the PCV valve into the intake tube. It was leaking like a sieve and causing a lean condition.
 

Phil II

Cone Destroyer
I should update this thread as it might help someone who is chasing P0171 and P0174 lean codes. The one vacuum line that I failed to check and that turned out to be a culprit was the hose running from the PCV valve into the intake tube. It was leaking like a sieve and causing a lean condition.
Thanks for following up. Sometimes its the little things.
 
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