RPM surges?

[Moparman485]

Hello everyone
I just finished redoing the top end and head gasket on my 1991 Plymouth laser 2.0 non turbo. The car starts right up an has very little smoke (still blowing the crud out from sitting). But I've got a problem. The previous owner said that it probably needed a new mass air flow sensor because when it was not in gear the idle would "surge". Luckily, my friend actually had an extra mass sensor from his car so I replaced the one on my car with his. However, I still have pretty hefty power surges. A better description would be that the idle speed fluctuates rapidly up and down while I do not have the car in gear. In gear the idle holds rather stable with very light variations and has no other leaks or concerning sounds. Any ideas what could cause this? I'm still new to DSM cars so I'm flying completely blind on this one.
Thanks in advance
JB

 

[92AWDHX40]

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge)

 

[dsmcurse]

the idle air controll thats built into the throttle body is more than likely dirty and in need of cleaning. also check for vacume leaks as this can cause it. these old cars wont ever idle perfect at like 600RPM like a litttle civic will. they need to have a bit faster idle. shoot for 900-1000RPM. also make sure cam angle sensor isnt to far advance. as this will cause your base timing to jump around a bit and then the idle air controll tries to take over and mork some magic and the two trade off back and forth from like 800RPM to like 1400RPM and this can be very annoying.

check for vacum/boost leaks, check base timing is correct, maybe pull throttle body off and clean parts inside, re-assemble and adjust base idle set screw for about 900 rpm

 

[luv2rallye]

http://www.dsmtuners.com/forums/articles-engine-fuel/191137-how-fix-your-idle-surge-problem.html

 

[Moparman485]

OK, il give a few of those a try. I just replaced the throttle body gaskets and I've checked them for leaks. I actually have an extra Throttle position sensor and an extra Idle air control valve. I will swap them out when I get to the house and hopefully that will fix her up. Other than the erratic idle it runs great so hopefully its not too painful of a fix. If I figure it out or find something different from that other list il add it on here

 

[luv2rallye]

Throttle body shaft seals is another very common leak area when they get old. A boost leak test will detect them. To replace: http://www.dsmtuners.com/forums/art...ody-shaft-seal-replacement.html#post151053750

 

[Moparman485]

Ok, so I swapped both the tps and the iac. Now it idles fine, but as soon as I put it into gear it dies. I played with the timing in all positions and regardless of how it is timed it still does the second it goes into gear with the new IAC but idles just fine. Any ideas?

 

[Metal Health]

Need to ground out the pin under the hood that will set the IAC to 0 then adjust your idle properly. Must have no boost leaks, its also a good idea to check your timing while your in there. The pin/connector is behind the battery its a black single wire connector, may still have the cap an tape on it.

 

[Moparman485]

Is it the one that looks like a large capacitor and is about an inch directly to the right of the wiper motor?

Also, I just unplug that one pin connector from the plug, hook it to a ground, start the car, an set the idle speed/timing. Could this be what is causing the car to die as soon as it goes into gear? The idle speed with the new iac is close to 2k and it still does as soon as it goes into gear. But, if I press the gas quickly after it goes into gear I can keep it running.