Rough Idle ....P0400
 

I have tried researching but still need more info if I may. I'm a 63 yo retiree but willing to do DYI and have time in my hands although back sometimes refuses to cooperate so please bear with me and hoping I get some reply to this post.

2000 Gallant 130k miles except for the current issue car is in excellent condition. Despite the rough idle it still averages 21-22 mpg and runs like a dream until I am on a stop light then it begins to shake. Temporary solution of course is put it in neutral.
It started doing this a little more than two weeks ago.

A two years ago a new EGR and solenoid was installed because "Check Engine Soon" light was on. It was all fine till recently when the light came on again but this time with a rough idle.

My neighborhood mechanic check it and said the solenoid was not grounded properly and fixed that problem and check vacuum hoses/connections and said they are all good but my valve cover gasket was leaking at the back side and needs to be replaced. Got that done but problem still persists, rough idle ( 70 % of the time) Sometimes it would just idle nicely. Mechanic said I have to change the intake manifold gasket since I have develop a gasket leak probably caused by being soaked in my oil leak. The diagnosis makes sense except for the following;

a) I thought a gasket leak is constant. I mean if that is the cause of the rough idle, it should be consistently rough, right?

b) I cleaned the intake manifold and everything around it and sprayed it with carburetor cleaner and the engine did not surge a bit, meaning no leak?? Right?

Since retirement funds are always low, I don't have the funds to support my mechanic's research on this issue and I am willing to do it myself.. Any help will be greatly appreciated!!

BTW, I'm in the Dallas area if you know a better mechanic.

Thanks for your replies!

ReySC

.P0400.....Exhaust Gas Recirculation Flow

Thank you Sir! I realize that however I just my question is will a leaking intake manifold gasket trigger a P0400 code ? A million thanks for your time and response.

OBD-II Trouble Code: P0400 Exhaust Gas Recirculation Flow Malfunction

Since the egr valve & solenoid are fairly new, it could be a bad line, faulty wiring or a defective valve or solenoid. Considering youre experiencing a rough idle, chances are either a bad line or one of the passages is severely blocked. If its a blocked passage, get some seafoam or a heavy duty carbon cleaner (gun section of walmart or cleaning section of sporting goods store). Hope this helps

Thanks again. I just need to get in there and pull out the EGR valve inspect and clean and go from there.. Will keep you posted and I will try to ignore the intake gasket leak diagnosis of the mechanic. I think that is the one that threw me off..

Thanks for the reply and your time is well appreciated!

ReySC in Dallas.

mikemitsu,

Just an update, we pulled out the EGR and cleaned it thoroughly with Seafoam. Looks almost new and nice and shiny and you can see the inside. It was black inside when we pulled it out. Check the diaphragm and it is working just fine. It ran smooth and idled well for 20 miles then back to the same issue....Could this be a Solenoid issue ? I'm running out of suspects. Thanks a again Sir!

What rpm is it at when it starts to get rough? & did the c.e.l come back on? What brand parts did u put in? A lot of the time aftermarket parts like that suck compared to o.e.m