the flyin' scotsman

When starting from overnight cold the car seems to be running on less than all 8. It wants a little help from the gas pedal to maintain a good idle then once it clears itself the engine smooths out and all's fine.

This only happens starting from very cold; all other starts are fine.

Intake has been refreshed and the TPS and ISV checked out fine.

Car has a warm engine high idle (possibly related if its a vac leak)?

SeanR

First guess would be Temp II/wires.
High idle might be due to vac leak or O2 sensor.

blitz928

+1

Lizard928

New plugs yet? Condition of cap and rotor?

the flyin' scotsman

Spark plugs are new this season.................caps and rotors have approx 35k kms on them.

Temp II was my first suspect.............it did ohm out ok a few seasons ago but haven't checked recently.

Stromius

Mine does this too and it's been the coil wire. Found a tiny bit of corrosion at the passenger connection.

John Speake

How high is the idle speed ? Steady or fluctuating ?

the flyin' scotsman

Idle is perfect tabletop smooth at ~1100 rpm when warm.

I just got back tonight from a +1100 km weekend trip and the car ran flawlessly except for the stumbling cold idle and high warm idle.

When first starting in the morning can the temp II signal be 'forced' to give a better signal? as a test I could swap out the OEM Temp II with one thats on the GT.

John Speake

Idle should of course be 675rpm under all conditions when hot. It's a closed loop system.

So an idle speed of 1100rpm shows the loop isn't under control.

When engine is cold the idle speed is still regulated but at a higher idle speed, which reduces to the normal 675rpm as the water temp rises.

Have you tried idle adaptation with your diagnostic tool ? And checked the operation of the Closed throttle switch with the tool ?

the flyin' scotsman

I would use the diagnostic tool to do these operations but you may recall I fitted PEMs to both ecu's.

I'll swap out the T2 sensor and report back.

John Speake

Ah ! Of course, silly me.... have you checekd manifold vaccum ?

the flyin' scotsman

I swapped the temp II sensor with the one from the GT which idled correctly...............the S4 started well from overnight cold but the high warm temp idle remains.............I'll check the intake vac John

SQLGuy

One thing you could do is the propane leak check trick... basically, you take an unlit propane torch, while the engine is idling, and wash the propane over areas where you think you might have a vacuum leak. Extra "fuel", in the form of propane, that gets sucked into the manifold will cause a drop in idle.

the flyin' scotsman

Car started this morning with the same results as before the T2 sensor swap.

On initial start it wants to stall without help from the go pedal. It sounds like its loud sucking air from somewhere under the intake which gets quieter as it warms and as its does warm the engine suddenly smooths out............like a light switch. If I disconnect the T2 sensor with cold engine running the loud sucking sound disappears.

John............I measured intake vacuum at the front fuel dampner. When cold readings were 12 in Hg and increased to +40 in Hg when revved. Once the engine warms and the stumbling ceases the vacuum reads the same 12 in Hg at idle with a slight decrease when revved.

There's something vacuum related when its cold thats the problem me thinks but resolves itself when the engine warms.

The high 1100 rpm idle remains.

John Speake

Hi Malcolm, Those vac readings seem too low, you should measure around 21inHg at idle......