98 2.0L Erratic Idle Problem
sentinal02
11-26-2009, 03:44 PM
Hi Guys,
Hoping someone can offer me a new perspective on this problem as it's go me stumped. for the past month I've been dealing with this problem on and off. finally broke down and took it to a shop only to have them tell me there's nothing wrong with it.the main problem right now is that the car has an intermittent loping at idle that has no set pattern that i can determine. one minute the car idles ok, the next it will drop to about 450 rpms on the tach, bounce back to 900 and keep going back and forth, almost stalling in the process. If you go down on the throttle, sometimes it will kick itself out of the pattern, and other times it will still run like crap all the time you're on the throttle. I've had it on my scanner watching the data in real time trying to find the point where it starts doing this, but i can't isolate it as one thing. TPS, MAF and O2 sensors read normal (ie the don't suddenly die like there's no signal from them), and the problem will happen whether the engine is hot or cold. the weird thing though all of this is that the computer will not throw out a code.
So far I've replaced the plugs and wires, coil test ok both hot and cold. originally the car didn't want to start when it was raining out so I originally suspected the plug wires. I recently changed the computer out and it seems to have helped the wet start as it started fine during the rain the other day, but it's still kinda early to tell. the idle issue is still there though. battery is new, alt is putting out fine even during the loping, fuel pressure tests good. my pressure tester won't give me a running pressure as it's one of those types that hold the highest pressure recorded until you push the release so i haven't been able to figure out if the pump is failing intermittently. the fact that i can rev the engine during the lope though seems to point at an ignition issue to me though and not a fuel starvation. anyone got any ideas before i start throwing sensors at it? I thought of the timing belt skipping teeth, but to me that should be a constant issue, not something that comes and goes.
Hoping someone can offer me a new perspective on this problem as it's go me stumped. for the past month I've been dealing with this problem on and off. finally broke down and took it to a shop only to have them tell me there's nothing wrong with it.the main problem right now is that the car has an intermittent loping at idle that has no set pattern that i can determine. one minute the car idles ok, the next it will drop to about 450 rpms on the tach, bounce back to 900 and keep going back and forth, almost stalling in the process. If you go down on the throttle, sometimes it will kick itself out of the pattern, and other times it will still run like crap all the time you're on the throttle. I've had it on my scanner watching the data in real time trying to find the point where it starts doing this, but i can't isolate it as one thing. TPS, MAF and O2 sensors read normal (ie the don't suddenly die like there's no signal from them), and the problem will happen whether the engine is hot or cold. the weird thing though all of this is that the computer will not throw out a code.
So far I've replaced the plugs and wires, coil test ok both hot and cold. originally the car didn't want to start when it was raining out so I originally suspected the plug wires. I recently changed the computer out and it seems to have helped the wet start as it started fine during the rain the other day, but it's still kinda early to tell. the idle issue is still there though. battery is new, alt is putting out fine even during the loping, fuel pressure tests good. my pressure tester won't give me a running pressure as it's one of those types that hold the highest pressure recorded until you push the release so i haven't been able to figure out if the pump is failing intermittently. the fact that i can rev the engine during the lope though seems to point at an ignition issue to me though and not a fuel starvation. anyone got any ideas before i start throwing sensors at it? I thought of the timing belt skipping teeth, but to me that should be a constant issue, not something that comes and goes.
fords4me
11-26-2009, 04:12 PM
I'm searching threads to find something to help me with my idle surge. My '90 Mustang is doing about the same thing. I read here that it may be the IAC(Idle Air Control Valve). I've cleaned as of now and no fix. Im thinking though, it may the the fuel pressure regulator. In fact I'm sure the regulator is bad because it seeping raw fuel into vaccum line, Im just not sure if the regulator would cause the surge. When I replace the regulator I'll let you know if it fixed my problem.
sentinal02
11-26-2009, 06:46 PM
I'm searching threads to find something to help me with my idle surge. My '90 Mustang is doing about the same thing. I read here that it may be the IAC(Idle Air Control Valve). I've cleaned as of now and no fix. Im thinking though, it may the the fuel pressure regulator. In fact I'm sure the regulator is bad because it seeping raw fuel into vaccum line, Im just not sure if the regulator would cause the surge. When I replace the regulator I'll let you know if it fixed my problem.
yeah, the IAC would have been my first guess too, but the 98 doesn't use one. I thought about the regulator but i haven't noticed a big gas smell from the vac system.
yeah, the IAC would have been my first guess too, but the 98 doesn't use one. I thought about the regulator but i haven't noticed a big gas smell from the vac system.
fords4me
11-27-2009, 03:08 PM
Ok, Just to reiterate, my '90 mustang's idle was surging. It would rev then drop, rev and drop. Sometimes it would stall, other times it would even out and stay steady, depending on how lond I stayed still. I noticed too while I was driving, it would feel like it was missing almost. Anyway I replaced the fuel pressure regulator today and my problem is solved:lol2:.
I believe the vacuum was sucking raw fuel into the intake and flooding the engine or at least upsetting the air/fuel mixture. I got this below off a website about a test of and symptoms of a bad regulator. Hope it helps. Whatever fixes your problem, please post about. It may be someone I encounter in future. Good luck.
Fuel Pressure Regulator Test
This test checks the operation of the fuel pressure regulator to make sure it changes line pressure in response to changes in engine vacuum. This is necessary to maintain the proper operating pressure behind the injectors and to compensate for changes in engine load.
With the engine running, disconnect the vacuum hose from the pressure regulator. As a rule, fuel system pressure should increase 8 to 12 psi with the line disconnected. No change would indicate a faulty pressure regulator, or a leaky or plugged vacuum line.
If the diaphragm inside the regulator is leaking, engine vacuum will suck raw fuel into the intake manifold through the vacuum hose (look for fuel inside the hose).
I believe the vacuum was sucking raw fuel into the intake and flooding the engine or at least upsetting the air/fuel mixture. I got this below off a website about a test of and symptoms of a bad regulator. Hope it helps. Whatever fixes your problem, please post about. It may be someone I encounter in future. Good luck.
Fuel Pressure Regulator Test
This test checks the operation of the fuel pressure regulator to make sure it changes line pressure in response to changes in engine vacuum. This is necessary to maintain the proper operating pressure behind the injectors and to compensate for changes in engine load.
With the engine running, disconnect the vacuum hose from the pressure regulator. As a rule, fuel system pressure should increase 8 to 12 psi with the line disconnected. No change would indicate a faulty pressure regulator, or a leaky or plugged vacuum line.
If the diaphragm inside the regulator is leaking, engine vacuum will suck raw fuel into the intake manifold through the vacuum hose (look for fuel inside the hose).
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