Poor idle, surging, almost but won't die

[Devsdaytona]

I did a bit of searching, but thought it may be worth a post.

Car is a 90 daytona VNT Stock

I put some injector cleaner in a tank ago with 92 octane and it seems that not long after the car would begin to idle erraticly once warm. When driving it is perfectly normal. Car would surge and then eventually drop down to just below 500rpm but wouldn't die, it would just chug away. I have recently replaced the oxygen sensor, rotor, wires and tried swapping another known good TB on with no change, there is a noticeable difference when I unplug the map sensor, no codes are present and I have tried reseting the computer, distributor timing is good, I can't find any vacume leaks either.

Tommorrow I'll be putting gas in it for the first time since the injector cleaner and maybe try a new fuel filter that I got for it awhile back, maybe run a propane bottle along all the vac lines.

Any advice from the wonderfully smart and helpful people who are members of the greatest tm site in the world.

Thanks

[Juggy]

check your throttle body sensors, the TB might even be really dirty in the AIS passage this could cause idle probs

car pulling any codes?

[Devsdaytona]

I have replaced the throttle body and sensors with a known good one.

I hope to finally have the time to replace the fuel filter tonight.

I have checked the fpr, timing(cam and dizzy), put the stock computer in, plugs, wires, engine bay vacume lines and tried pinching of the boost gauge and heater control.

If I pinch of the fuel rail line it dies and when I pinch of the regulator fuel line it will idle up and then die.

If it's chugging and dies, trying to start it right away it will just die immediatly, if I let the pump prime atleast twice it will start right up and idle normal for a bit.

thanks

[Force Fed Mopar]

Sounds like a speed sensor problem.

[Devsdaytona]

changed the fuel filter and rechecked the vac lines, including heater and boost gauge, still no change, speedo works, no codes.

I'm running low on ideas

thanks

[Dusty_Duster]

Sounds like a speed sensor problem.

+1

Have you checked the speed/distance sensor? Mine came loose, and I used a zip tie to hold it in. I'll replace it, one of these days.

[JuXsA]

spray some wd40 in the TB

[Devsdaytona]

I'll have to check that out for sure.

Thank you.

[Devsdaytona]

Sensor passed the visual inspection, at no point has the speed or trip meter stopped working, there is still no codes. Also did another quick check of the vac lines and replaced a few possibly bad lines, but still no change.

Driveability and power is normal, just makes drive throughs and red lights very anoying

Me very confused.

thank you

[black86glhs]

Have you checked the map sensor itself?

[Devsdaytona]

yeah, tried a different one too.

[black86glhs]

Darn, I was hoping that was it. I am having a similar condition with my S.

[Devsdaytona]

Darn, I was hoping that was it. .

hehe, I agree

[89daytonacs]

anybody think it could be a clogged return line? we were tossing this idea around today

[Force Fed Mopar]

Check the fuel pressure, if the return is clogged the pressure will be higher. What amount of vacuum is it pulling? Vacuum leak maybe?

[Devsdaytona]

vacume is normal, I'll have to check the fuel pressure today.

Thank you

[87glhs]

Yes, check the fuel return line. Best place to do it is where the rubber line attaches to the chassis hard line down by the tank. Careful about blowing into the line using compressed air though as there is usually a small diffuser on the end of the tube in the tank.

When we had the problem our car would start, idle fine for 1min or so, then idle rough (opening throttle would make no difference) and die. We could then wait 1min or so and it would restart and do the same thing.

Result of old gas in the tank--had to pull the sender out and clean the tube with a piece of steel wire.

[IROCNOROLL]

But it runs normal off idle. Return line issues would affect it off idle as well as at idle. Also he has restricted the return line at the rail manually, with the expected results.

[Devsdaytona]

It runs great at all points once warm except when your foot is fo the gas at a stop.

I'm not sure what next, still need to check the fuel pressure I guess.

[89daytonacs]

ya know, my old civic used to idle really horribly most of the time, but usually wouldnt shut off, and it ran well at all other time (as well as civics run). after i broke my timing belt and gave it to my buddy, he replaced the belt and it idled perfectly after. maybe check into the last replacement date of your timing belt devin?