Team-BHP - Inconsistent idling and engine shut off problem

For the past few days, i am noticing some strange problems:

1.When the car is cold started in mornings, the idling is inconsistent. That is, the revvs rise up and down intermittently. I don't have tachometer but i can clearly make it up from the engine sound.
2.Again during idling, if i switch on the AC, the engine shuts off. This happens occasionally say when i am turning ac on/off at traffic signals.

Can these both problems be interrelated ? Maybe AC switches off when car at idle because engine revvs not able to completely support the Load.

Few points:
1. The WR has done 50k and is 5.5 yrs old.
2. I recently had the car for 5k service, but decided to change the engine oil, air filter,fuel filter and brake oil as well. However these problems were not apparant days immediately after service.

Either ignition is wrong or injection is wrong.
Check :

1) Injectors
2) Throttle body
3) Idle valve ( sorry if term is wrong ).

I don't know what 4 is called, but there is some small device or valve that controls the idle ( to the best of my knowledge ).

Thanks for the responses.

But..

Quote:

Originally Posted by sgiitk (Post 1475616)

Try cleaning up the injectors and the air filter.

this was already done at the last service (1k kms ago). Got a new air filter too (MGA).

Quote:

Originally Posted by Pankaj401 (Post 1475634)

Also get the IACV (Idle Air Control Valve)checked. It's this part that is responsible for increasing the idling rpm if the engine load increases.

hmmm.. but how does that explain inconsistent RPM during idle. That is, rpm going up-down-up-down on its own at idle. Ideally in cold start it should first increase and then gradually settle down.

Quote:

Originally Posted by aaggoswami (Post 1475647)

Throttle body cleaning and injector cleaning was already done last service.

Quote:

Originally Posted by DCEite (Post 1475859)

hmmm.. but how does that explain inconsistent RPM during idle. That is, rpm going up-down-up-down on its own at idle. Ideally in cold start it should first increase and then gradually settle down.

Well the IACV is used to let more air in when the engine is cold. As the engine warms up the IACV gradually closes. If the actuator for the valve is inconsistent in operation than that would mean erratic opening/closing.

Also when you switch ON the AC or Headlights the extra load that is presented to the engine is compensated by increasing the RPM. This is achieved by opening the IACV.

Quote:

Originally Posted by Pankaj401 (Post 1476046)

Well the IACV is used to let more air in when the engine is cold. As the engine warms up the IACV gradually closes.

Hi Pankaj, the Idle Air Control Valve operates whenever your idling, i.e. whenever your throttle butterfly is completely closed - its the IACV which allows enough air to bypass the throttle butterfly to sustain idle. The IACV has to work no matter what the temperature is.

DCElite, the IACV is controlled by the ECU & has to increase idle when the A/C is switched on. Proper operation of the IACV, or atleast its "duty cycle" can be checked using a voltmeter or a Tech-2. The workshop manual has a separate section regarding maintenance & troubleshooting of idling issues.

The IACV valve can stick due to crud build-up or enthusiastic cleaning of the throttle body. When the IACV is not responsive enough the engine's idle speed can see-saw or even switch-off. If the IACV is innocent, you could check your PCV valve.

P.S. - Amit had a nice thread regarding a similar issue, the final few pages should help...

Quote:

Originally Posted by im_srini (Post 1476349)

That's correct. Just wanted to emphasize that IACV needs to open further from it's no-load idle setting to compensate for the AC load.

When the engine is cold it opens more to raise the RPM and then gradually returns to idle settings.

Quote:

Originally Posted by Pankaj401 (Post 1475634)

Also get the IACV (Idle Air Control Valve)checked. It's this part that is responsible for increasing the idling rpm if the engine load increases.

Quote:

Originally Posted by Randhawa (Post 1475650)

I think Pankaj is spot on, look for any broken vaccume pipe.

Quote:

Originally Posted by Psycho (Post 1476236)

It is a case of a cracked / disconnected vaccum pipe look at the right side of the intake manifold should be easy to spot.

+1
I had this problem also and a a cracked vacuum pipe was the culprit.

Quote:

Originally Posted by DCEite (Post 1475529)

...car is cold started in mornings, ...the revvs rise up and down intermittently.
...during idling, if i switch on the AC, the engine shuts off.

Can these both problems be interrelate.

Broken/cracked/leaking vacuum pipe is the most likely culprit. Check closely.

Quote:

Originally Posted by archat68 (Post 1478908)

+1
I had this problem also and a a cracked vacuum pipe was the culprit.

Hi Guys,

Today my indica got truned off suddenly at the red light :Frustrati. At that time the A/C of the car was also switched on and all of a sudden I noticed a spike in RPM meter and thereafter the needle came down to zero.

After that the engine also got turned off suddenly. I am wondering as to what could be the reason, is this something that needs immediate attention or should I face for the next routine service which is anyway due in next month.

Thanks in advance
Pradeep