Engine revs up when started, surges when warm

[jaymack77]

Hi, I just acquired a 1995 Metro 1.0 auto. Drove home fine, until I filled the empty tank with $10 of gas. When I started out again on the highway, the engine was revving high, and pushing the car along. Stopping was a chore, and required both feet on the brake. When coasting on the highway, the car idles up and down (surges) , but is fine if you're punching it. When starting from cold now, it just begins to rev higher and higher until you shut it off. The car sat for quite awhile before I purchased it, and had a bit of a moisture problem inside. I have replaced the fuel filter, PCV, wires and plugs, checked the vacuum lines (to the best of my ability), tested the isc (plugged it with finger to check), played with the Throttle Position Sensor (seems ok). So I am unsure where to go next. Could a fuel pump cause the overrev? High idle controller? Fuel Pressure Regulator? I am at a bit of a loss- your insight would be most welcome! Many thanks in advance.

Jeff McLean

[GM Line Rat]

Read this thread explaining idle issues.

http://www.automotiveforums.com/vbul...d.php?t=749180

[jaymack77]

Thanks- I have been studying that article and working through it for the last day or so- I just don't know the location of the high idle controller or the fuel pressure regulator. And it seems funny to me that it would begin this funny action right after I fueled it up from an empty tank. (odd to go from perfect to problems after a fuel up) Some of the vacuum lines have small cracks in the end of the lines, but it revs right up as soon as it is started- not like a small leak. I'm stumped.

Jeff

[91Caprice9c1]

Check to see that your throttle cable is not caught awkwardly around the lever at the throttle body -shrugs- worth a shot - I've had it happen to me.

It would take a massive vacuum leak to achieve what you're describing. Does your brake booster hold vacuum? With a vacuum pump, attach it to the brake booster where the hose would normally go and see if it holds 15-20in.hg.

Get a fuel pressure reading. You will need to acquire a gauge and adapt it with a T fitting in line with the larger diameter fuel hose at the TB.

Take off the air filter housing and have a glance at the butterfly valve, see that it is tightly attached to the shaft and properly positioned.

Take a can of brake cleaner (or starting fluid) and spray generously around the intake manifold/head seam and vacuum lines. Listen for a change in engine speed. Don't do this if the engine idles way too fast to let is sit and run on its own.

The fuel pump on these cars cannot fail in such a way as to cause this condition. And it would be a stretch to have the FPR cause something like this in such a dramatic fashion. A clogged return fuel line would cause similar conditions as a stuck FPR, but again, it's really unlikely, but get a gauge reading anyway.

While you're looking at the butterfly valve, have someone turn the key on but not start it, and see if your injector is leaking fuel when it shouldn't be.

Goodluck.

-MechanicMatt

[jaymack77]

OK, it's fixed. I replaced the MAP sensor and ICS with ones from the wrecker, and no fix. While I was at the wrecker, I grabbed the whole throttle body (including the MAP and ICS) for $30. I installed the new throttle body, and it runs like a charm. I have no idea what it fixed, but who cares, it worked!! Maybe the Fuel pump regulator (I think that's internal) A huge thanks to all who took the time to respond to my enquiry. you guys are angels in disguise!!

Blessings,

Jeff