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-   -   700 RPM Idle cold, 400 RPM idle hot. (https://www.viperalley.com/forum/showthread.php?t=121746)

Red1994 July 26th, 2013 03:36 PM

700 RPM Idle cold, 400 RPM idle hot.
 
The car tries to stall every time I pull up to a stop light if I down shift through the gears. New K & N air filters, Mobil 1 10-30 oil. 94 gen 1, 17k, fresh plugs and wires, on a battery tender. Starts hard cold but starts harder hot. 4-5 second crank time hot.
What's the cure?
Thanks.

Matty July 26th, 2013 05:52 PM

How old is your battery and are the connections clean and tight? Is it bogging down while it is cranking and then speeding up as it cranks? Meaning is it slow out of the gate and builds up steam until it fires?

MoParEr July 26th, 2013 09:05 PM

Your battery my have one foot in the grave, do you know it's age? Even with a tender, it will not last forever. When it's dead, you will know it. But that idle thing, sounds like a air/fuel and/or sensor problem. As for the cure, a good mechanic and a few grand. Good luck with that.

dave6666 July 26th, 2013 09:36 PM

Could be a fuel pressure issue or throttle body problem.

Matty July 27th, 2013 12:09 AM

I'd start with the battery and work your way up the expense chain......good luck

Netko July 27th, 2013 03:21 AM

IAC?


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Red1994 July 27th, 2013 05:59 AM

Quote:

Originally Posted by Matty (Post 1880170)
How old is your battery and are the connections clean and tight? Is it bogging down while it is cranking and then speeding up as it cranks? Meaning is it slow out of the gate and builds up steam until it fires?

Cranking speed is fine which is why I hesitate to drop $180 for a new battery if it cranks well.

dave6666 July 27th, 2013 06:27 AM

$180 battery? I pay $120 @ AutoZone for a Duralast.

1badvr4 July 27th, 2013 09:14 AM

Quote:

Originally Posted by Red1994 (Post 1881042)
Cranking speed is fine which is why I hesitate to drop $180 for a new battery if it cranks well.

What's the volts read at the battery post while cranking? I would clean the IAC first.

Username July 27th, 2013 10:27 AM

Disconnect ECM for a while and then re-synch throttle bodies both on the cable and to ECM.. You can take IAC off and clean/oil while you're at it.

Red1994 July 28th, 2013 04:59 PM

Quote:

Originally Posted by Username (Post 1881314)
Disconnect ECM for a while and then re-synch throttle bodies both on the cable and to ECM.. You can take IAC off and clean/oil while you're at it.

Do you have a step by step procedure for this? I hate to admit that I'm a low tech old fart in a high tech shit storm.
Thanks.

Username August 16th, 2013 09:17 AM

Quote:

Originally Posted by Red1994 (Post 1883634)
Do you have a step by step procedure for this? I hate to admit that I'm a low tech old fart in a high tech shit storm.
Thanks.

Battery disconnect is a no brainer... while it's off, open hood, look on side of both throttle bodies where the cables attach, there is a button-like device, press it in and pull the cables back .. Once you have done that, slowly and firmly press the accelerator pedal all the way down and you will hear the cables ratchet back down. Next, reconnect battery, turn ignition on and press accelerator pedal slowly down to floor 3 times, turn ignition off and then back on, start engine. IAC is bolted to forward, upper r/s of engine.. has a hose and a harness and 2 or 3 bolts. Take it off and spray inside with a little WD40 and reinstall. You can leave harness plugged in to check operation as you clean it but it might take a few cycles to reset after.

EllowViper August 16th, 2013 11:37 AM

Quote:

Originally Posted by 1badvr4 (Post 1881282)
What's the volts read at the battery post while cranking? I would clean the IAC first.

This...since your injector duty cycle references battery voltage both during crank-run-restart cycles. In layman's terms, your ECU adds or subtracts injector duty cycle based on battery voltage. You may have cranking voltage, but it saps the needed voltage to adequately power the injectors...or once running, a low voltage is telling the ECU to add injector duty cycle since the injectors will lag in their functioning. THis can result in some strange running conditions when coupled with other low voltage induced compensations. Add in the "key on" voltage settings the ECU uses to calibrate most of the 0-5v references...you can see how a weak battery can effect more than just cranking the engine.

Red1994 August 17th, 2013 06:28 AM

Quote:

Originally Posted by Username (Post 1920266)
Battery disconnect is a no brainer... while it's off, open hood, look on side of both throttle bodies where the cables attach, there is a button-like device, press it in and pull the cables back .. Once you have done that, slowly and firmly press the accelerator pedal all the way down and you will hear the cables ratchet back down. Next, reconnect battery, turn ignition on and press accelerator pedal slowly down to floor 3 times, turn ignition off and then back on, start engine. IAC is bolted to forward, upper r/s of engine.. has a hose and a harness and 2 or 3 bolts. Take it off and spray inside with a little WD40 and reinstall. You can leave harness plugged in to check operation as you clean it but it might take a few cycles to reset after.

Thanks. I think I can handle that. I cleaned the IAC. It wasn't that dirty but I cleaned it anyway. It didn't make any difference. Seeing it is in the fuel system I used carb cleaner. Should I have used something with some lubricating properties?
Thanks again.

Red1994 August 17th, 2013 06:34 AM

Quote:

Originally Posted by EllowViper (Post 1920474)
This...since your injector duty cycle references battery voltage both during crank-run-restart cycles. In layman's terms, your ECU adds or subtracts injector duty cycle based on battery voltage. You may have cranking voltage, but it saps the needed voltage to adequately power the injectors...or once running, a low voltage is telling the ECU to add injector duty cycle since the injectors will lag in their functioning. THis can result in some strange running conditions when coupled with other low voltage induced compensations. Add in the "key on" voltage settings the ECU uses to calibrate most of the 0-5v references...you can see how a weak battery can effect more than just cranking the engine.

Thanks for reinforcing the battery thing. I guess a new battery is in my future. I'll see if I can get some voltage readings on the battery before I pull the trigger on a new one.

EllowViper August 20th, 2013 01:33 PM

You want around 13.8v running...

virginiavenom August 20th, 2013 01:47 PM

we only use B12 in our shop to clean IACs, just getting some of the crap out of there usually does the trick, usually if it cranks fine, and voltage running is good, but a dip when turning on the AC and recovers when the AC is turned off you might need to replace the IAC....rare, but it happens. it is a pretty old car. unplug your IAC and repeat the on/off of the AC and tell us if there is any difference to when the IAC is plugged in. if there isn't than I'm betting an IAC problem assuming the battery is good.

Red1994 September 23rd, 2013 10:08 AM

Quote:

Originally Posted by Red1994 (Post 1879978)
The car tries to stall every time I pull up to a stop light if I down shift through the gears. New K & N air filters, Mobil 1 10-30 oil. 94 gen 1, 17k, fresh plugs and wires, on a battery tender. Starts hard cold but starts harder hot. 4-5 second crank time hot.
What's the cure?
Thanks.

I had to replace the IAC. Now it starts better hot than it does cold. Once again it's fun to drive, but alas, no more fun for me this year. Back surgery tomorrow.
Thanks for your help.


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