Strange problems....sort of

[screnshaw400]

Hi all!

I have been plagued with problems with my '99 sho. I have been trying to deduce the problems one by one without breaking the bank, and I still have not gotten any headway...... For starters: The car starts fine most of the time, the other few times it starts sputtering like it is going to stall out (possible fuel or ignition related.... ran codes plenty of times and not getting anything...). When the car is in park, the rpms will rise and fall between where it is supposed to be idling at and about 1000 rpms and that is pretty much all the time. When that happens, I believe I hear the idle air control valve making a clicking sound like a solenoid. I had the cams welded, and to tell the truth, I really didn't have a good chance to listen to how it ran before due to how quickly I wanted the cams welded up (who can blame me!?). I have replaced plugs (not coils....I know, I should), fuel filter, air filter, pcv valve, and just the other general stuff.... When I have some spare time, I plan to ohm out the o2 sensors, try to ohm out some of the coils and things like that. Anytime that the car is driven, it runs perfectly fine and I can't seem to notice anything like a misfire or things like that, but the car gets really sh*tty fuel mileage (at worst I am averaging about 200 miles to the tank, and that is with conservative highway driving (about 20 miles each way to work) and I pretty much average between 17-20 mpg on the highway. I know that a lot of the responses will state to check the common things that I have already mentioned, but if someone who has experienced the same problem as I have and has the exact remedy, that would be awesome! By the way, the car has about 65K on it, so its not like it has been driven into the ground......even though I sometimes drive it spirited (surprise! who doesn't! maybe the old lady that owned the car before me....) Sorry about the long, run on paragraph.......Thanks!

 

[LJRuddy]

As for the rough idle, does it do this after a long drive where the engine has plenty of time to heat up? I have this issue but only after I have driven it aggressively. What happens is the fuel rail (which is pretty much dead middle of the engine) gets hot and the fuel inside of it begins to evaporate leaving air pockets. Cycling the fuel pump once or twice will usually solve the issue.

The high/low idle is a common problem on gen 3 SHOs. In fact, there was a TSB posted about it many years ago. I have found that spraying some electrical contact cleaner into the IAB connector solves the problem for a short while.

As for the bad MPGs... Does your car run fine in the higher RPM?

Thinking out loud here but your rough idle could be related to your poor fuel mileage. A loose, broken vacuum hose would cause rough idle and poor MPGs.

 

[screnshaw400]

Thanks for the quick reply! The rough idle is not really dependent on driving conditions, as it has happened when I have started the car in the morning after it has been parked for the night and it has also happened after driving the car over 200 miles on the highway. On the IAB valve, I have cleaned the idle air control connector and the valve itself, and the problem did not disappear. The vacuum hoses that are common that I have done some research on were dryrotted and replaced. A co-worker that used to work on cars over at roush also told me to check the camshaft sensor, but my idea is if the camshaft sensor was on it's way out, it would exhibit more, how you say, drastic problems as a no start issue. I really would like to figure out this problem out on my own, but due to time constraints with turning 50-60 hour work weeks and going to school full time, I just can't find the time to turn a wrench (or a multimeter), which sucks. I have had some reputable people tell me to check the coil packs, but as again, the front ones would be a piece of cake......the rears are another story.... I just might try to find the time to take it to the local ford dealer to have them do a cylinder balance test to rule out that.....ahem......costly repair. With the o2 sensors, generally aren't they pretty much good until at least 75K? I just don't get it, with the car sometimes acting like it is about to take a crap for a second, I was thinking that it might be fuel related (i.e. fuel pump), but I don't get any starvation at higher rpms at all. This isn't anything that inhibits me to getting to work or school, I just would like to have this thing solved before it turns into something that is a lot more expensive and bites me in the ass!

 

[bacernate]

swap #5 and #8 coils and see if you get any difference. a failing #8 coil can really mess with the maf sensor. Have you cleaned the maf sensor? If it's dirty it will overfuel at idle and run lean at higher rpm.