3.2 Surge and stall issue when idling
 

I've got a new issue I'm trying to figure out.

A few weeks ago I replaced my fuel pump but I'm pretty sure it's not related.
The car ran fine for a couple weeks without issue.

When I cold start the car it seems to idle fine for about a minute, then it start to surge between 800 and 2000 and finally stalls. After stalling it won't start for until the car goes cold again.

Checked all the connections in the engine bay and everything is tight and all the clips are three.
I replaced my fuel filter today also.. No difference.

I'm thinking maybe head temp sensor? But I recall replacing it about 3 or 4 years ago when I had the engine out...

Any suggestions on what to test/look at?

Thanks
-Dan

I had a similar problem last year and it ended up being the idle control valve on my 3.2 which I had replaced. It fixed the problem. There is a good video of the same problem (maybe not fully stalling). https://youtu.be/MRZG-s_55CU

Classic symptoms of vacuum leaks.

Yes. Check the hose from the oil tank to the rubber boot on the throttle body. Mine was doing the same thing.

I did find one disconnected vacuum line, but it didn't resolve the problem. I'll have to look around some more.. http://forums.pelicanparts.com/uploa...1595169540.jpg

Tighten all the bolts holding down the intake runners. They can get very loose over time. Mine did. Can vacuum leak like crazy.

You can also get vacuum leaks at the manifold where it meets the head. If you have access to a smoker it makes finder the leaks easier.

Where's the best place to plug in for Vacuum leak checking.. The brake booster port?

I built A smoker from YouTube out of pvc and although it worked awesome I didn't find any leaks.
Next step is test switches.

I rechecked all vac hoses and tested the resistance on the head temp sensor. Both were fine.

Bump for suggestions...

Did you clamp off or plug the hose to the brake booster? It's a long hose and can have splits or cracks in it that are out of sight.

Did you check the intake manifold to head nut's as suggested?

Also, the gaskets at this point can suck in and leak around the perimeter.

Typical of a bad temp sensor, just use a paper clip to temporary bypass it shortly after the engine warms up.

yes. Intake manifold head nuts were checked.

Maybe try checking the voltage as the car is idling. If the voltage fluctuates a lot the sensors output will be affected. The amount of fuel will change if the voltage feeding the injectors is changing.
Also, look at the fuel pressure, if the fuel pressure is not steady it will make an even bigger difference than unsteady voltage.
Another also, I wonder if the MAF could be sticky.

If anyone is interested here's an update.

Fuel pressure was good, although it does bounce a bit between 30-35 when running.

Fuel Volume test was good.

Compression on all cylinders was around 180 so that was good.
Plugs were black due to being too rich. I replaced them while I was there.

I have to have the CHT sensor plugged in to start it, but after a minute when it warms up it'll start to go rich and surge and stall.

When the engine is warmed if I just jump the CHT with a paperclip it will idle fine and is driveable. But the resistance on the CHT is accurate when both cold or when at running temperature.

Since I have a cat bypass I installed a Wide Band O2 sensor which is awesome and is showing me how the mixture looks.

http://forums.pelicanparts.com/uploa...1600993587.JPG

Here's the one I installed.
https://www.ebay.com/itm/AEM-30-4110-AFR-52mm-Wideband-O2-UEGO-Controller-Gauge-Air-Fuel-Ratio-4-9-LSU/261571397731

We think it may also have been running rich for a long time.

More to come....

Is the closed throttle micro-switch doing it's thing? Test the two terminal plug with an ohmmeter, should read open/closed. The idle control valve won't kick in if the switch doesn't tell the computer that the throttle is closed.
Also, too high or too low idle speed can create a surge, as well as too rich.

I just helped get this engine sorted out yesterday, met up with Dan in person.

Primary issue was an intermittent CHT sensor, worked fine cold but as soon as it started to warm up it would go open circuit. When this occurs the sensor reads infinite ohms and the DME thinks engine is extremely cold (-30C) and then DME dumps extra cold start fuel via the injectors causing excessive idle hunt.

We replaced the CHT and this cleared up the main issue.

However, the injectors were also not working properly and resulting in over fueling at idle most likely bad spray patterns. I then installed my inj+chip package into this motor:

http://forums.pelicanparts.com/porsche-911-technical-forum/888986-new-product-performance-chip-matched-injectors-3-2l-carrera.html

Then calibrated the system and the engine now runs fine with these new injectors and the special calibrated chip for these injectors.

Found a bunch of other wiring issues, the 3.2L transplanted motor was not properly done. Fixed up the fuel pump wiring so the pump no longer runs all the time. The pump had not been wired to the DME relay, instead they simply powered it any time the KEY was in RUN or START.

Also found other wiring not properly done, left a list of this to be fixed in the near future.

In summary: engine had faulty CHT sensor and injectors with bad spray patterns.

The WBO2 gauge Dan installed is a MUST have to help get these motors properly running. You can use this gauge to set base mixture and even test injectors while engine is idling.