# Idle coasting vs Idle stationary



## twincam6 (Jul 30, 2008)

1.) What factors control engine idle speed? Of those factors, which would be different when the vehicle is coasting vs when it is at rest?

2.) Here's the scenario: The truck's 2.4 (1994, manual trans, 2wd) idles fine at startup or whenever parked. When it's being driven and is coasting to a stop, the engine idle drops to around 250 rpms or even dies. If it doesn't die, the idle returns to normal only after the truck comes to a complete stop.

3.) The only code is 55 - no detectable errors.

4.) The TPS ohms measure within range and change with throttle movement.

5.) I found the TPS hanging up a bit, rubbing against a drooping wire. After moving that out of the way, there was no longer any last second "snap back" that I noticed while under the hood. A test drive proved disappointing - the problem was still there.

6.) I found a small vacuum hose with a crack. I replaced it with new - no change.

7.) The counterman at the auto parts store suggested checking the one-way valve leading from the brake booster. I did; it was fine.

8.) Several months ago I had an intermittent problem with the speedometer. It would read a little high on the highway and then not read anything below about 45, just dropping to zero. The problem went away and hasn't returned in about a year.

9.) Occassionaly, at startup, the engine stumbles briefly when revving it slightly, until the engine warms. This acts like a bad TPS but, again, I am not getting any codes but 55.

10.) Referring back to bullet number 1. I can't think of anything that is different when rolling other than input from a VSS or whatever sensor measures air coming into the throttle body, but I"m not getting any error codes. I'd rather not go down the path of component replacement by trial-and-error. Do any of you know what might be causing this?

11.) Thanks!


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## Grug (Aug 20, 2009)

Not too knowlegeable in this area, but could it be a faulty MAF? Check out this MAF post from another Nissan site.

How To: MAF Cleaning for a better running engine! - Topic Powered by Social Strata


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## zanegrey (Dec 5, 2005)

start with fuel filter and a good tune up...

verify the fpr vacumn source maybe route it to a manifold source..


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## twincam6 (Jul 30, 2008)

12.) MAF sensor looked clean. I cleaned it anyway with CRC MAF Sensor Cleaner and replaced the air filter. No change.

13.) Zane - a fuel filter would not cause the low idle under such specific conditions. However, it was on my to-do list anyway so I replaced the 200,000 miler with a new WIX. Of course, no change.

14.) Vacuum at idle is vacuum at idle. It would not change with the speed of the vehicle at idle.

15.) Timing. Mitchell says 8-12 degrees BTDC. Haynes (my less trusted and usually more frustrating source) says on 1990+ timing is ECU-controlled and there is no owner-adjustment. That is supported by the lack of timing marks by the crank. The fact the distributor has a range of adjustment in the mounting bolts tends to support Mitchell's assertion. I'm stumped.

16.) Interesting condition: If the speed is kept below 15mph and the rpms below 1500 the problem does not occur.

17.) Observation: while running engine with the TPS unplugged, the revs are limited to 1800.

18.) This MUST be a sensor issue yet I get only code 55. Anyone else?

19.) Thanks again.


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## zanegrey (Dec 5, 2005)

try lube the pivot points and lubing the return spring or mechanism for the throttle ..

as it sits the vacumn source is most likely routed thru or in concert with a vacumn switch.. try it straight to a manifold source..

if it works good if not put it back..


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## SOBS (Jul 20, 2008)

Currently having a similiar problem ...

Here is a solution I found on another thread "Just figured i would let you all know my problem is fixed. ended up being a bad crush on the gasket between throttle body and the intake manifold. Basically a bad vacuum leak. all fixed and back going."( http://www.nissanforums.com/hb-truck/158109-problems-after-timing-chain-loss-replace-2.html


I've also got to check the 
IACV-ACC valve or cracked vacuum hose. Wish both of us luck.










http://autorepair.about.com/library/faqs/bl421a.htm


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## SOBS (Jul 20, 2008)

Researching this.... "Ignition Timing adjustment Mode" I'm still researching it's a setting in the Work Support Mode of the Engine Control System. Still trying to figure out how to do it without hooking it up to a diagnostic computer.
Update! *29 Mar 09*


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## rogoman (Dec 16, 2004)

twincam6 said:


> Here's the scenario: The truck's 2.4 (1994, manual trans, 2wd) idles fine at startup or whenever parked. When it's being driven and is coasting to a stop, the engine idle drops to around 250 rpms or even dies. If it doesn't die, the idle returns to normal only after the truck comes to a complete stop.


Several things to check:
- O2 sensor may be bad.
- Fuel pressure may be incorrect.
- IAA valve may be dirty.
- Intake manifold vacuum. Use a vacuum gauge - reading should be around 21 InHg.


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## SOBS (Jul 20, 2008)

Love the Avatar Rogoman

After messing with mine all day with a similar problem I've discovered. #1 do not use carborator cleaner on the carborator the MAF does not like it. Luckily I used alcohol on it and got it to work again. (whew) 

Rogoman makes some very good suggestions but let me add just one more that I came across today. When reinstalling the MAF make sure the seal seals #1. #2 the TPS make sure you put it back on and ajust it (its very sensative also). Mine was off just a little and my truck refused to idle. I'm almost done. Ok back out there hopefully the last round of this fight. If you don't here from me the final adjustments on the TPS worked.


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## rogoman (Dec 16, 2004)

SOBS said:


> Love the Avatar Rogoman
> 
> After messing with mine all day with a similar problem I've discovered. #1 do not use carborator cleaner on the carborator the MAF does not like it. Luckily I used alcohol on it and got it to work again. (whew)


Thanks for the comment

In regards to cleaning a MAF, you lucked out. I've talked to a lot of people that screwed up their MAF by improper cleaning.

Use only ELECTRICAL CONTACT CLEANER or a cleaner specifically made for MAF hot wire cleaning. This is the only thing you should use to clean your MAF. No windex, no carb cleaner, no brake cleaner, no rubbing alcohol, and no Q-Tips.


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