bouncing tach in neutral

[Sexymeatball]

Ok, so im driving back from boston and stop at a toll booth cause i hafta. Well, i cruise in from about 10 or 15 in first, put it in neutral and coast in to the toll booth. Well, as im waiting to get my change back, the tach needle starts bouncing up and down and the stupid car almost stalls at around 200 rpms This obviously makes me sad and embarrassed so i had to floor it coming out of the toll booth to regain my dignity naughty In any event, this wasnt the first time this hasnt happened, but it has never almost stalled in traffic. It is an intermittent problem and is exasperated by the fact that my car starts hard after it stalls (a few cranks). This is due probably to the fuel pumps discharge valve as pointed out by the all knowing and ever helpful sdpatt (thanks again if your reading this). I just gotta find the time and cash to replace the pump with a walbro. In any event, what could be causing this bouncing idle? It happened when i first got the car, but cleaning the MAF fixed it real quick. Any suggestions would be great. Thanks

 

[musiccitysho]

Is there any chance youre idle needs to be reset?
If not it sounds like what my ATX was doing before I removed the IAC and cleaned the plunger with carb cleaner.
It started with the bouncing idle once or twice, then a week later it kept stalling out right after starting it unless I maintained the idle manually with the gas pedal.That maybe a drivable condition for a MTX but not an ATX. A quick fix I stumbled onto was pulling the jumper prematurely during the KOEO test, this at least got the car to hold an idle which was enough to get me home and pull the IAC.
Also I had no codes present or CE light during this condition

 

[SHOPWR]

my bouncy idle was my IAC in which i cleaned and it helped but i still had a bouncy idle and i ended up changing my HO2's cause they were bad the way it was. and sure enough, i regained my good gas milage back and my normal idle speed.if you have not bench tested your HO2's i would do that to check and see if they are lazy.

 

[Sexymeatball]

HO2's? Do you mean 02's or is this a sensor i dont know about? In any event the O2's arent more then a few thousand miles old so they're not the problem. Ill clean the IAC and see what that does. Thanks for the advice.

 

[Porkchop]

I tried cleaning my IAC out and unfortunatly it was too far gone to try to resurrect and make work so I had to order another one.

Through Advance it was a little more than $70 for a new GP Sorensen one - runs perfectly now. If you put your cleaned sensor back on and it doesn't fix the idle issue - bite the bullet and get a new one. I farted around for too long trying to save my old one.

 

[PROPHET]

It may be a vaccum leak, i would check the vaccum lines by the rear valve cover by the canister on the intake that controls the seconderies.

 

[SHOPWR]

HO2'S (heated oxygen sensors)

 

[Sexymeatball]

Well the IAC is cleaned and back in and that doesnt seem to be the issue, so maybe its too far gone as porkchop suggested? In any event its still an on and off problem that never seems to occur when im trying to diagnose it (only when im trying to make left hand turns in the middle of a busy intersection). In addition, i got a hold of a fuel pressure gauge, and to my surprise the fuel pressure was at optimal levels while priming, at idle and reving. This was not quite what i was expecting but i cant say its unweclome. It also doesnt add up that my pump is fine but there was no pressure at the rails 15 min after turning it off while changing the fuel filter. Im not sure if this contradicts sdpatts theory or if its still a possibility. So now i need to try to figure out why it takes several cranks to start sometimes (usually only after stalling) if its not the fuel pump. sigh...If i had more money, more time, and more expertise then both my SHO and I would be very happy.