Another thing to take a peek at is the function of the EGR valve if you still have one.
Run a vacuum line separately down to the vacuum actuator on the valve and put a mouth vacuum on it until it retracts completely to check that there are no air leaks in the diaphragm. Quickly release the vacuum to allow the spring to bust any carbon that might have accumulated on the valve seat inside. Do that a couple times with the engine not running. The manual test for the EGR valve function is to start the engine and then apply a vacuum to the diaphragm at idle. The engine should stall. To test the vacuum modulator follow the test procedure in the book but a real quick check is to apply mouth pressure to the connection on the bottom. If there's a leak in the diaphragm inside the modulator, air will pass through. Otherwise, it should hold pressure if it's working properly. I had a problem with a hole in this diaphragm which caused the engine to run funny at speed with no load on. It felt like the engine was pulling and pushing. When I replaced the defective vacuum modulator, the problem went away.
|