Eval system, VSV and EGR valves

JOHN MURRAY2

MEMBER
2000 TOYOTA COROLLA
1.8L
4 CYL
FWD
MANUAL
238,000 MILES

Hello, first let me say, I am not a professional, but I am experienced. So anyway my problem stems from misfire codes. Specifically a multiple random and cylinder four. I have all new spark plugs, gaped, and moved ignition coils around with no luck. I have new fuel injectors, and replaced the one on cylinder four. I have had the car for months, and I believe the fuel filter is pretty new. Maybe it was fuel pump. So I am convinced my problem comes from the vacuum system. The two parts in question, are located on the air filter housing. (I can unplug the VSV and EGR, get no new codes, and engine sounds the same) When I test the line off the throttle body, I have perfect vacuum presser (21 mg). Put that line back onto the VSV, and the exit line has 10 mg ( it is also a constant vacuum, never stops and receives a constant four volts, with no change). Hook that back on, and the line into the EGR has almost no vacuum. If I hold my finger on it for a while, it will barely pull after a minute. If I unhook the vacuum lines, it will run worse. The closest vacuum lines will stall the engine out.
1) is the vacuum pressure supposed to be at 21 through the whole system?
2) how can I make the computer turn these on? If I unplug both, I can start it, warm it up, idle it, full throttle it, and the engine never sounds different.

1 Reply

CARADIODOC

MECHANIC
33,916 POSTS

There should not be any vacuum going to the EGR valve at idle or low road speed. That would cause a rough idle from lack of oxygen in the mixture. If you have eliminated spark as the cause of the misfires, an EGR valve that is not sealing closed is a good suspect, especially if the engine runs well at highway speed.

To operate the EGR valve, on some models you can simply apply vacuum to the port while the engine is running. For those that are electrically-operated, you can use a scanner to talk back and forth with the Engine Computer, and command it to do it. Some scanners won't let you do that function while the engine is running or while the vehicle is moving.

If you can not feel the misfires that are being detected, a good suspect is mismatched injectors. Chrysler buys their injectors in flow-matched sets from Bosch, and rarely has a problem. GM just grabs a handful of injectors from a huge bin and throws them in the engine with no regard to flow-matching them. That doesn't cause a problem until the engine has high mileage, then they start to flow at different rates. One or two will flow less than the others and cause those elusive misfire codes. Toyota never really had problems with their injectors, but it pays to keep that in mind.