EGR Valve Mystery?

The check engine light on my '89 Geo Metro came on and has stayed on for the past few weeks, occasionally turning off by itself for a little while and then coming back on again. When I flash the codes, it comes up 51, which is Exhaust Gas Recirculation Circuit. I did all the tests in the Chilton and all the components: Value, Modulator and VSV seem to be working fine. I checked the vacuum coming from the throttle body which was 0 in. Hg at idle, but went up to 10 in. Hg or so as I pushed down the accelerator.





Should the vacuum be 0 at idle or does this indicate a vacuum leak?





When I put 10 in. Hg of vacuum on the ERG valve itself when running it moves drastically and the engine runs very poorly. When I warm up the car and put the vacuum gauge on the hose going to the EGR valve, I see that it does get about 10 in. Hg when I push the throttle down.|||Some EGR valves work off a differential pressure balance so they operate differently on the engine than off engine on a vacuum tester. Many times the EGR passage ways into the intake manifold get clogged up too. I've had to have the intake manifold cleaned on some Fords I own.|||The valve is open at idle, responding to the higher vacuum and lower demand for fuel ,as the throttle opens and rpms(along with demand for fuel , the valve should close.


Your problem is probably the sensor for the Egr. It's a cheap part 15-30 bucks.


I'd r+r that first.|||Generally (and I mean generally), this is an indication that one of your pollution control sensors is intermittently going bad. Time to take it to a qualified mechanic.|||The EGR only opens under moderate thottle with a "load" on the engine.(in drive)





There are three points of vacuum.


1) Manifold vacuum. (high at idle)


2)Throttle vacuum (high at high speeds)


3) Ventury vacuum (a mix of the two above)





The EGR primarily controls detonation durring cruising speeds in conjunction with timing advance.





You could have a plugged port to the EGR valve. At idle, the engine should die if the EGR valve is actuated.|||It seems you have a vacuum leak...the vacuum at idle should be between 18 to 22 inches vacuum, closer to 22 usually. If you are checking by pulling the vacuum hose off the throttle body, and putting the gage there, you should get full vacuum at idle.





Check to see your throttle body bolts are tight, then you may have to take it off and check under it to make sure there isn't carbon/dirt built up under it.|||possible 0/2 sensor