03 Focus Running Very Rough
First, an apology. This is going to be a long initial post but I want to give you everything that I know because I'm hoping somebody out there has had this problem and fixed it.
The situation: The car has 85,000 miles, has an automatic tranny, and the small 2.0 I4. It's run great until about a month ago. Now, it runs very, very rough (most of the time). By rough, I mean it's much louder than normal and there is an intense vibration at all RPM levels. It's most notable at idle but still apparent when driving. It never stalls. The problem doesn't go away once the car warms up but when warm it is slightly better at idle than when cold. The vibration is so intense that the dash rattles. No check engine light yet.
Here's what makes it really weird. Running the car around for a while and then parking it in the garage for about half an hour seems to fix the problem. Under those circumstances it runs like a dream, smooth and quiet. My only guess is that the problem isn't related to operating temperature but to the temperature of the engine compartment itself. Sitting in a garage with no wind, hood down, and a hot engine right in the middle seems to solve whatever is causing my problem.
The background: Less than a year ago we had my mechanic replace part of the EGR system. We were hearing a loud exhaust like noise but the exhaust pipe and muffler looked fine. The mechanic said I had a crack in my exhaust relay pipe. He replaced it and while it was in there we had him change the plugs and wires. It ran fine after that.
Since the current problem started in the last month I've done the following:
1. replaced the air filter
2. replaced the PCV valve
3. inspected the PCV hose and connectors (nothing wrong)
4. ran a tank of gas with fuel injector cleaner
5. tested the EGR valve by pulling the vacuum hose off the top, and blocking the hose. The idle didn't smooth out. I applied a vacuum to the EGR valve manually and the car immediately stalled which tells me that the EGR valve itself is working fine.
All of the online forums pointed to a fault in the EGR system or a hole in the PCV hose as the likely culprit. I'm certain the PCV assembly is not the problem. The EGR system might still be the problem but not with the valve itself. The vacuum pressure going to the valve puzzles me. I read that there should be no vacuum applied at idle and there was a pulsing sort of pressure coming from the vacuum hose. I don't know if that matters or not since the problem didn't seem to get better when the vacuum hose was completely separated from the EGR valve.
At this point I'm guessing that there could be a problem with the EGR sensor itself but more likely I have a pinhole in a vacuum hose somewhere. Maybe when the vacuum hose itself gets warm enough it becomes expands to close off the very small hole that's causing the problem?
Any guesses here would be greatly appreciated.