# 1993 Sentra does not hold idle at cold startup



## SQuaLZ (Feb 4, 2013)

Hey everybody.

My 1993 Sentra XE had problems with the idle where it would fluctuate and usually stall when I was stopped.

I recently put a new throttle position sensor as well as cleaned the IACV.

Every since, whenever I first start the car in the morning. It can't hold the idle and I have to start it about 3 times for it to hold. Also, about the first 10 seconds of driving it, the car feels like it is lagging really bad, then it drives fine afterwords.

It is weird because I used to have a problem with the idle once the car warmed up and it was fine on cold startup, but now it is the opposite!

Any insight would be greatly apprectiated.


----------



## Centurion (Sep 5, 2002)

I used to get that chronic cold surge and as a bonus pinging at part throttle under light load. I now use Techron and Top Tier fuel and the problems have gone completely away.
Lesson learned: don't use cheap gas.


----------



## smj999smj (Jan 1, 2006)

You could have a bad IACV-AAC valve, which is used to control cold start fast idle and to help maintain idle during load conditions (headlights, P/S, A/C). It is important the base idle is properly adjusted per the FSM procedure in order for the IACV-AAC valve to operate properly.


----------



## SQuaLZ (Feb 4, 2013)

How do you adjust the IACV? I just took mine out, cleaned the gunk out and reinstalled. I didnt even know you could control the idle with an adjustment on it. Do I also have to adjust the TPS I installed?


----------



## smj999smj (Jan 1, 2006)

TPS adjustment:

Start the engine and warm to operating temperature.
Using a volt meter, check the output voltage between terminals as shown.

If the voltage is between 0.45 - 0.55 VDC at idle, the sensor is adjusted properly.
If the voltage is not between 0.45 - 0.55 VDC at idle, proceed to step 3.

Loosen the throttle sensor securing screws.
Rotate the sensor until a voltage of 0.45 - 0.55 VDC is measured between the terminals at idle.
Tighten the screws and disconnect the harness connector for a few seconds, then reconnect it.

-------------------------------------------------------------------------
IGNITION TIMING

Start the engine and warm it up until the water temperature indicator points to the middle of the gauge.
Operate the engine at 2000 rpm for 2 minutes under no load.
Disconnect the throttle sensor connector.
Idle engine and check timing. Timing should be 10°±2°BTDC.

If not proceed to step 5.

Idle engine and adjust the ignition timing to 10°±2°BTDC by turning the distributor after loosening the securing bolt.
Turn the engine off.
Reconnect the throttle sensor connector.

----------------------------------------------------------------------------------
NOTE: Before attempting to adjust the idle speed, perform a basic under-hood inspection. Check and verify the condition of the following:

Air cleaner
All vacuum hoses and ducting for the intake
EGR valve operation
Gaskets
Throttle valve plate and throttle bore for carbon
Throttle switch/sensor operation.

Disconnect the throttle sensor harness connector. Start the engine and warm it up until the water temperature indicator points to the middle of the gauge.
Operate the engine at 2000 rpm for 2 minutes under no load.
Race the engine 2 or 3 times under no load, then check the idle speed. Idle speed should be:

USA M/T vehicles only.
650 ±50 rpm.
Canadian M/T vehicles only.
750 ±50 rpm.
All models with A/T transmissions.
800 ±50 rpm (in "N" position).

If not correct, proceed to step 4.

Race the engine 2 or 3 times under no load then idle.
Verify ignition timing is 10°±2°B.T.D.C.


Turn the idle adjusting screw (located on the idle air adjusting unit) to obtain the correct idle speed. Idle speed should be:

All M/T 600 ±50 rpm.
All A/T 725 ±50 rpm.

Turn the engine off.
Reconnect the throttle sensor harness.
Race the engine 2 or 3 times under no load then idle. Idle speed should be:

USA M/T vehicles only.
650 ±50 rpm.
Canadian M/T vehicles only.
750 ±50 rpm.
All models with A/T transmissions.
800 ±50 rpm (in "N" position).

If not correct proceed to step 11.
Check the A.A.C. valve and harness, repair or replace as required.
The ECM may be the cause of a problem. This however is rarely the case.


----------



## rogoman (Dec 16, 2004)

SQuaLZ said:


> How do you adjust the IACV? I just took mine out, cleaned the gunk out and reinstalled. I didnt even know you could control the idle with an adjustment on it. Do I also have to adjust the TPS I installed?


The IACV has an idle adjust screw. Follow SMJ's procedure. If the engine does not idle fast when it's cold, the 'air regulator' component of the IACV may be bad or the harness connector is not secure.


----------



## b13er (Apr 7, 2010)

The IACV Air Regulator is what adds more air during cold startup. It's not where your normal idle air control is, but inconveniently located under the intake manifold.

My guess is that the valve is sticking. It's not weird because if the valve got stuck open, once the car warmed up, your idle would be way too fast. It must have worked one more time but is now stuck closed, so you aren't getting that extra air when the engine is cold. So it makes perfect sense to me and even helped diagnose the problem.

---------------------------------------------------------

Rockauto calls it an axillary air valve and it's $60. Here is a picture of it: More Information for AIRTEX 2H1234

To test it start the car (engine should be 100% cold) and then pinch one of the hoses that go to it. If the idle doesn't change then it's bad. Normally the idle would drop when you pinch it.

You might be able to just clean the old one by shooting lots of carb cleaner in there. As hard as it is to install though (removing the top half of the intake manifold and possibly even needing new intake manifold gaskets), you might just want to spring for a new one.


----------



## ryan (Apr 24, 2004)

There are no pictures. I need to adjust my idle. 



smj999smj said:


> TPS adjustment:
> 
> Start the engine and warm to operating temperature.
> Using a volt meter, check the output voltage between terminals as shown.
> ...


----------

