98 Crown Vic Barely Running!! :o( - Page 2 - Ford Forums

evuguys · 07-06-2009, 15:51

Forgive me for asking, but how do you get a vacuum reading? I haven't tried that yet! Is there a special piece of equipment I need?

**rtg143** · 07-06-2009, 22:33

You need a vacuum gauge and connect it to a port on the intake. You can also connect it to a tee in the system that comes from the manifold.

evuguys · 07-07-2009, 08:05

Thanks! I'll give that a try and give you an update as soon as I find something out.

noboston · 07-09-2009, 14:30

how many miles on this car ?? maybe a clogged exhaust system.I had a ford taurus that would bearly run and replaced the catalyst converters , only to find it would not start because the muffler was plugged.replaced muffler , end of problem

evuguys · 07-09-2009, 15:30

144000. I keep getting the OBD2 code for "Catalyst Efficiency Below Threshold Bank 1". Could that be the culprit? Also, on a side note, I can't get access to any vacuum gauges or anyone that has any, so I'm not sure what the vacuum pressure is. But, I have been looking under the hood of a few 98 crown vics this last week and they have all had the IAC replaced recently (each one was nice and shiny!) and mine looks like it could be the original one. My question is, I know the IAC valve would affect the engine quality at idle, but would it also affect my highway engine quality, because the problem is there sometimes as well.

Thanks!

noboston · 07-09-2009, 17:51

is this car a former police car that may have more time on the engine then the miles indicate??how strong is the exhaust flow?? you may have to replace the maf sensor,iac valve,and the throttle postion sensor(tps).have you check the fuel filter, fuel pressure??all of these things could affect your rpms , idle and power.

evuguys · 07-09-2009, 17:58

Yes, it's a former police car. I am suspecting the IAC may be the culprit, but I'm not sure. With it being a police car, I'm sure it idled more than a normal car, so it may have gave the IAC valve a severe workout. I'm no mechanic! The cat converters are not original, though, I do know that. The exhaust feels strong when its running right.

fixitnowlt · 07-09-2009, 20:31

I think you have more than one problem going on here.

Definitely replace the IAC valve. When you do make sure you clean the throttle body with intake cleaner. Any commercial brand will do. You can have someone hold the accererator pedal to the floor to open the butterfly or hold it open with a screwdriver. Removing the return spring will help. If the throttle body is really dirty on the inside, get jiggy with it. Use an old toothbrush and rags. Clean it till it shines.This may cause a hard start after cleaning but just gas it up to clear it out.

FYI- An EGR valve that is stuck open can cause a rough idle. This valve should only be open at highway speeds. There may be carbon built up that is holding it open.

As for the check engine light. If it is a P0420, you need to replace the catalytic converter assy for the right side. No bones about it. It has nothing to do with the flow or volume of exhaust. The front o2 sensor and the rear o2 monitor are compared by the PCM and determine if the cat is doing its' job. They are not doing their job anymore and cannot chemically break down the oxides of nitrogen. Prepare to spend $400-$500 for the part.

evuguys · 07-09-2009, 23:17

Thank you so much for your informative reply!!! I will do those things and hopefully that will fix it. I replaced the EGR valve about two weeks ago, so it should be ok right? Again, thank you!! Thanks to everyone else who replied as well. I will update after these suggestions are tried.

evuguys · 07-11-2009, 15:46

Well, I replaced the IAC valve today and cleaned the throttle body, but still no luck. Any other suggestions or ideas?