1987 Ford E350 Corsair EGR Question ?

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Nov 23, 2019
Hi all,

Thought I'd try this forum again as in the past I got some super helpful info from members. Awhile back I was having some issues with my RV, mainly with lack of power and some other performance issues. The list of things i did was:

- first a compression check, 125 psi all across the board. Installed new plugs
- replaced fuel pump and fuel filters
- Fixed all broken vacuum lines
- new carburetor

And the last thing I did was put on a new EGR valve. The rig then sat for a couple months and the other day I was back at it and first it took forever to get it started which is not a problem I ever had. Then once going the idle was super rough, surging up and down and then stalling a few times before it warmed up. Even warmed up the idle still would slightly surge up and down. So checked out a few things and then thought of the last thing I did, which was put the new EGR on. So I tried unplugging the EGR vacuum line and the idle went pretty much back to normal. Plugged the line back in and the idle dipped so low it almost stalled. So I decided to throw the old EGR back on and now the thing purrs like a kitten, no issues at all. I should have prefaced all this with I didn't find a problem with the old EGR just thought while i'm at it may as well put a new one on.

So just wondering if anyone knows why that would happen ? From what I've read if an EGR valve is stuck open it'll cause poor idle but unplugging the vacuum line shouldn't fix a stuck open valve ? Unless I'm missing something here. Also when i had it unplugged I did plug the vacuum line and EGR hole and it still idled fine, although from what I've read there is no vacuum at idle anyway. That said it also idles much better with the old valve on. So we're kinda at a if it ain't broke don't fix it stage but I'm just curious now as to why that would be, maybe someone out there who knows more than me ( which is probably most on here ) might be able to chime in.

Thanks in advance!


Well-known member
Nov 8, 2009
Check using a timing light. A worn timing chain can cause all sorts of drivability issues.


Well-known member
Jun 25, 2018
If you have a vacuum pump or you can plug it into another vacuum line with the engine running, you should be able to see if both the old and new valves close/open like they should. You could also have a bad vacuum temperature switch or somebody mixed up the vacuum line routing.

No need to replace the old EGR if it tests ok. If it is frozen shut it idles fine but being stuck closed can reduce gas mileage and cause an engine knock under load. But sometimes just a good cleaning with carburetor cleaner and a wire brush will free it up.
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