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So I've finished installing the new intake.

All is well, but once I rev the eninge and release the idle drop below 600 rpm, almost stalls and goes back up.

What's most likely the cause?

Air in coolant? Coolant lines of throttlebody have been off but cooling has been bleeded...

Vac leak? Idle does not surge.

IAC? Worked before swap, same iac.

Any suggestions?

It's probably your IAC. The little black round thing under your throttle body.

You can try to unplug the white connector and see if it still happens.
Sometimes it works do disassemble the complete TB and clean the inside, re-tune the tps and idle screw.

Anyways... getting a good idle can be a pain !

My guess is vacuum leak somewhere. Double check vacuum lines and the things connected to those lines. All those vacuum lines make the K series engine a pain to troubleshoot erratic idle. If vacuum lines are good then do the tune up stuff:
Set the TPS using a digital multimeter (look in the service manual if you haven't done this recently).
Follow tune up instructions for setting idle and timing.

With the coolant lines disconnected from the IAC it really does nothing. All the IAC does is provide high idle when coolant is cold and TPS indicates throttle is closed.

Air in the coolant will cause erratic surging idle. But my bet is vacuum leak.

You can also check the web for methods to find vacuum leaks like spraying some brake cleaner / throttle body cleaner / propane around the intake looking for leaks.

Ok i'll check again.

TB has been cleaned.

So I disconnected IAC, the idle changes a little (I think, barely noticeable)

How much is supposed to change in rpm?

Air is definitly out of the system.

Can't seem to find any vacuum leaks.

Assuming:
TPS is adjusted properly
Idle is adjusted properly. When the engine is warm idle is steady and around 650 - 700 rpm.

What is new intake? Is this just a cold air system or entirely new intake manifold?

Maybe the problem is really simple and in your new intake the VAF is in a funny position. The VAF is best mounted so it is horizontal (not pointing down or vertically mounted) and the connector and tab need to be in a plane that is parallel to the ground. Sitting on your throttle body looking at the air filter the VAF connector is on the left and the mounting tab on the right.

Tps had been adjusted, idle is steady.

A complete New manifold had been installeren (klg4).

Vaf is horizantally installed, connector is correct.

Things i've noticed:

Problem is less when warm, but still there.

When shutting off the engine the brakebrooster immediatly loses its Vacuum. Pedal pumps up.

Jforce wrote:Tps had been adjusted, idle is steady.

When shutting off the engine the brakebrooster immediatly loses its Vacuum. Pedal pumps up.

This happens to me too.I don't know if this is a problem or this is the way it should work..

It's not normal, wasn't like that before.

Would also be strange, what if your engine stalls on the road. You would immediatly lose your power brakes(sure u can still brake, but you need more pressure than u expect.). Overnight yes, immediatly I think not.


Although i don't quite understand how a booster keeps its vacuum.

If you track the booster, the air can move freely from the nipple of the booster to the manifold, to the throttlebody and out the intake??

Another guess since you installed the KLG4 manifold: Did you cap off what looks like a vacuum line nipple but is actually exhaust that feeds a boost sensor in its original application?

I don't have a good picture, but it is a nipple on the manifold rear bank (cylinders 1, 3, 5 nearest to cylinder 5), behind injectors and also near the throttle body. You need to cap it. Do not attach a vacuum line since there is no vacuum provided.

Regarding brake booster:
Yes you do lose vacuum essentially immediately after the engine stops running since it is the source of vacuum. However the brake booster vacuum line should include a check valve so that air movement is one way - always toward the intake manifold.

Unless the brake booster vacuum line is leaking it should not impact idle with or without the check valve.

davmac wrote:Another guess since you installed the KLG4 manifold: Did you cap off what looks like a vacuum line nipple but is actually exhaust that feeds a boost sensor in its original application?

I don't have a good picture, but it is a nipple on the manifold rear bank (cylinders 1, 3, 5 nearest to cylinder 5), behind injectors and also near the throttle body. You need to cap it. Do not attach a vacuum line since there is no vacuum provided.

Yeah its capped.

Brake booster vacuum line has no check valve.

It's just a hose, not oem. But it wasn't oem with the Curved Millenia intake either.


So far:

- No leaks to be found using any ghetto method

- All vacuum hoses have been replaced

- The IAC has ben checked Ohm is according to spec in manual between 10,7 - 12 or something

- Everthing was in working order before swap, so unlikely that the iac broke (i think)

- Tps is adjusted

- No Air in Cooling system

- Haven't adjusted idle screw, same throttlebody not necessary? Should idle the same as before, no? I don't have anything to measure exact rpm. So I went on needle, which is in the same position as it was before and rock solid.

To be continued...

Well the brakebooster problem is fixed.

Apperently the valve is actually in the stock hose, so replacing with silicone was bad lol.




De idle problem remains...

Found any solution?

For the brakebooster yeah, using the original hose fixed it.


For the idle drop, no still does that.