Another Fox-specific Technical Question...
 

Alright, needing a little diagnosis help from other Fox owners...

Driving around and engine braking the car makes huge vacuum and overall runs great but at idle it's rough, stumbles and just generally runs like shit. The vacuum will sit around 15-16 and as it stumbles drops to around 10, it'll catch itself and the nasty idle continues. Now I've looked over vacuum lines and they all look good, I have a few of them capped off so it doesn't take much to check them. IAC looks clean, MAF was inspected a couple thousand miles ago but may be due for cleaning, fresh plugs/wires a couple thousand miles ago.

My plan is to buy a new cap/rotor and see if it's ignition related (the car sat for ages before I got it and the contacts inside the cap are a little burnt) but I don't really have the money to be throwing parts at something. Is there generally something on a Fox that causes this or am I just gonna have to dig into it? Does the EGR valve if it's bad cause a vacuum leak at idle that may cause these symptoms? Any suggestions would be great!

Stock ecu? Is it tuned? Whats base timing? Idle rpm? Iac voltage? If idle rpm is too low, itll drop too low and hunt forever. What i used to do is put my foot on brake and let clutch out to catch the idle. U can also raise idle or base timing, both of those help too. Or get a cam with less lope...

TrueStreet tuned it, ran great 'til a couple days ago so something called it quits. CEL came on after lunch today so gotta get the codes pulled and see what's up. It's had an intermittent problem with a soft miss at cruising speeds that I never could place as the problem was so intermittent. So I'm placing my bet on EGR system..

Do you have an msd ignition? If the msd is bad it will cause this.

Ignition is second on my list, had a suggestion at TrueStreet about o2 sensors that I hadn't thought about so I jacked up the car and crawled under it and they're mismatched and old as hell. Since I've had intermittent CEL's and the problem manifested as if something failed I'm gonna go with the o2's as a first point to try then move on to ignition.

Replaced the o2's and cleaned the IAC but no real change. Idle improved marginally but still stumbles from time to time. Car is also almost undriveable in the rain/real high humidity. It'll shudder under low throttle situations... ignition related? Cap/rotor look nice enough and plugs/wires are new. MAF is also on my list to clean, just such a pain in the ass to pull it on this car..

Spray electronic cleaner under cap and see if it improves when dry? Sounds like an old school moisture problem. Small crack in underside of distributor housing maybe???

TP Sensor?

So let me get this straight... you had a car that ran great and then started throwing CEL's and you came here to ask why and said you'd randomly start troubleshooting the problem throwing money at stuff that may or may not be bad but you wont check the codes that will tell you where to look?

http://sbftech.com/index.php?PHPSESS...a&topic=2471.0

Thanks for the smart-ass reply, the CEL was exceedingly intermittent, leading me to believe it was caused by something external to the car and not a constant issue with something on the car itself. The rough idle developed with no connection to the CEL, I could see no real correlation between them. For the record, I cleaned the MAF, unplugged the battery to wipe any adaptations and now it is back to it's normal self. We will see if the problems comes up again next time it rains. And the only money I 'threw' at the car was on o2 sensors to replace the mismatched ones that the previous owner must have pulled from a pile of trash and put in...

It wasn't a smart-ass reply, it was an honest question. Have you done the tests in the link I provided? It's basic troubleshooting, and while it might be intermittent it will at minimum give you a list of stuff to look for first. If you want, I'll shut up as it seems you might not actually want honest feedback.

Honest feedback/help is great. I guess I'm conditioned from other forums to think any reply worded similar to yours is being a smart-ass about it. Lol. I have not done those tests, I was under the impression that the only option you had with OBDI was to read the codes when a light was on, I was not aware it had functionality beyond that. I will read it, thanks.

Good deal, let us know what you find.