90coman Posted February 2 Share Posted February 2 1990 with a 2.5 won’t run without the vaccum line on the MAP sensor unhooked. It will start up and then idle down and die. When I rev it up and try to hold RPM it will surge up and down. With the line unhooked it runs good but if I try to drive it doesn’t seem to have power. I replaced the sensor with a new one. And still no change I tested the MAP and it tests good. Anybody know of some things that can cause this. Thanks in advance. Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 2 Share Posted February 2 Something tells me the ISA isn’t adjusted or working. That motor on the front of the throttle body pushes the throttle plate open to allow a proper start up and control the idle. That’s one problem. another one would be the manifold bolts. Another would be TPS or grounds. Link to comment Share on other sites More sharing options...
pizzaman09 Posted February 3 Share Posted February 3 The manifold bolts seem very likely based on the symptoms. Or any large vacuum leak. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 3 Share Posted February 3 Link to comment Share on other sites More sharing options...
90coman Posted February 8 Author Share Posted February 8 Put a new valve cover gasket on it and still no fix. I tested the TPS and the adjustment is right and it reads proper continuity. It still will only run with a vaccum line unhooked. I did notice that when I unhook the line on top of the vaccum tree that is threaded into the back of the intake and then hold my finger over the opening it will kill the motor. The vaccum line goes to the solenoid on the passenger side fender. Could the solenoid be my issue? Link to comment Share on other sites More sharing options...
gogmorgo Posted February 8 Share Posted February 8 Creating a vacuum leak allows the engine to run, stopping the leak kills the engine. That’s what you’re suggesting? The solenoid on the passenger side is for cruise control? Maybe? I’m not sure it’s relevant though. Because the engine running with the vacuum leak happening and the dying without the vacuum leak happening seems irrelevant to whether the solenoid is connected to a vacuum source or not. If you hook everything back up and crack the throttle slightly (slight pressure on the gas pedal) when you try to start it, does it stay running until you let go of the gas? If yes, you may need to adjust the ISA. It shouldn’t have been touched, but someone may have done something trying to solve some other issue. There’s a procedure linked a couple times in another active 2.5 thread right now. I’d also be curious what your air filter looks like. Its probably not the case but if its caked up and blocking all air flow it’ll also cause running issues. You’d likely see a collapsed intake tube. Mud, dust, snow, ice, or even heavy or prolonged smoke could plug it easily enough. Adding air via either gas pedal or vacuum leak can also correct for a severe over-fueling problem. Pulling a spark plug and checking for rich operation or raw gas on the plugs would be the diagnostic technique there. Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 8 Share Posted February 8 7 minutes ago, gogmorgo said: The solenoid on the passenger side EGR solenoid is on that side. OP valve cover gasket wouldn’t be your issue. Link to comment Share on other sites More sharing options...
90coman Posted February 8 Author Share Posted February 8 Sorry I meant intake gasket. And also yes the EGR solenoid is what I am referring too. With everything hooked up it will not run without me giving it gas. And when I try to hold rpm it motor with surge up and down. Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 8 Share Posted February 8 Check your EGR. See if it’s not gummed up and sticking. Link to comment Share on other sites More sharing options...
90coman Posted February 9 Author Share Posted February 9 Seemed to open and close just fine by hand. Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 9 Share Posted February 9 Did you test it while it’s running? Just to make sure the solenoid isn’t opening it already at start? Link to comment Share on other sites More sharing options...
90coman Posted February 9 Author Share Posted February 9 Yeah I did and it stays closed on start up. When I try to open it by hand it kills the truck. Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 9 Share Posted February 9 Ok the EGR circuit is fine. That’s good. Link to comment Share on other sites More sharing options...
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