1993 Buick Park Avenue Surging at idle

1993 BUICK PARK AVENUE
230,000 MILES • 6 CYL • FWD • AUTOMATIC
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SMARSACK
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I have a surge, only at idle. The car runs great down the road. Takes off well etc. It was throwing an EGR code before this issue so I changed the EGR (pintle was stuck open) and cleaned the throttle body and mass air flow sensor. Now it seems to lobe at idle but not a misfire. I checked voltage for the TPS, removed, tested and cleaned the IAC, and checked fuel pressure (44psi) and even checked the pressure regulator (pinching return line). There seem to be no vacuum leaks that I can hear or react when sprayed down with carb clean. Any ideas?

Thanks!
Apr 6, 2010 at 8:09 AM
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JACOBANDNICKOLAS
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Honestly, without the check engine light, it becomes a guessing game. Chances are it is the idle air control valve, throttle position sensor, or a vacuum leak that was missed. However, without a code, you need to check everything.
Apr 7, 2010 at 7:52 AM
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SMARSACK
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Well, the TPS starts at .35 volts and ranges smoothly to WOT at 4.05 volts. The IAC seems to function correctly. I took it out and cleaned the tip, turned the car on and it moved in and out...whether that range of motion is correct is to be determined. I replaced the PCV and it seemed a little better. I gently sprayed carb clean into the throttle body and it smoothed out. I pinched the fuel return line to test the fuel pressure regulator. Without a full size diagnostic machine (not just a snap-on scanner) that I can hook up, I'm a little lost. I can't see what carbon emissions (sniffer) are coming out the tail pipe but it smells to me like it is running a little lean. If it were running rich, I would assume a worn cam with this many miles. Thanks for your time...I will let you know what happens.
Apr 7, 2010 at 9:14 AM
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JACOBANDNICKOLAS
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The iac and tps sound good. With the engine off, if you remove the vacuum hose from the regulator, is there any gas in the hose?
Apr 7, 2010 at 10:26 AM