the flyin' scotsman

The '90 GT is up and running but has a very high idle.

All vac lines and connectors are new as is the throttle cable. MAF is 'old' as is the ISV. MAF connection was double checked, tight. All vac hoses were double checked, good. The ISV was lubricated via the WD40 method vac line method.

Idle stability tests were done with Theos diag system..............all good.

The t.cable was disconnected.............no diff.

Would a very bad MAF or ISV be of issue? something else?

John Speake

Does engine vacuum measure OK ?

the flyin' scotsman

John............I measured vac at the front fuel damper; its approx 14"hg.

John Speake

That suggests a airleak into the intake, you should get ca 21inHg. Airleak ca cause highi idle speed.

IcemanG17

14" is too low...try this test....get a can of brake clean and carefully spray it around the intake-air routing...give it a quick blast and if the idle goes up....theres a leak....if everything is sealed it won't change the idle..... Simple, but it works

the flyin' scotsman

thx John and Brian...............I just ran the drive link test through both ECUs............both had 1 fault each............Temp II sensor...........good that be it?............I cant change it as the engine is red hot.

Brian............I'll try the brake cleaner test..............I go through the stuff so much I buy it by the case

I should add the hi idle is rock steady.

Stromius

Malcom I had a slightly high idle post intake R&R and noticed as I poked around that the breather hose that goes from the oil filler at the base to the passenger side Y valve has hung up on the throttle spring slightly. Maybe just a simple thing..hoping anyway.

Might also test the vacuum with some smoke. I suggested on RM that you could use R/C airplane smoke pack in conjunction with the intake contraption Dwayne wrote about using Home Depot plumbing parts to push smoke into the intake to mimic the VacuTech machines that some shops use.

Hope it turns out..

the flyin' scotsman

ok.............I tried the brake cleaner test............idle was affected when sprayed close to vacuum splitter that goes to brake booster. I swapped the 'Y' piece but it didn't fix the issue. Now I'm thinking the cleaner was getting into the plastic piece thats fixed to the throttle boot.

thx Stefan, I'll look closely at that hose.

Waiting for it to cool off before trying again...............appreciate any more thoughts.

BTW............WARNING...............only use non-flammable brake cleaner, you can imagine what happens with the alternate.

the flyin' scotsman

Problem is getting worse

A new can of brake cleaner I sprayed everywhere under the intake.............no change.

As the engine heated further and the fans kicked on the engine is now surging between 12 and 1600 rpm.

The ISV runs through its cycle when tested with the diag tool.

IcemanG17

its very possible that one of the larger vac lines under the intake is leaking.....but it really doesn't take much unmetered air to raise the idle quite a bit......when I installed the intake spacers I didn't use enough "make a gasket" and there was leaks on one side....the idle was consistantly around 1100-1200

the flyin' scotsman

so.............off comes the intake again?

I'm going to look closer at Dwaynes intake pressure tool.

Bill Ball

Are the two lines that come off the throttle housing (one feeding the air pump diverter valve, the other the gas vapor recirc valve) still attached to the throttle housing? Gentle tug would verify. Also, it's easy to forget to attach the hose that goes onto the front of the throttle housing from the oil filler neck and gas vapor circuit.

the flyin' scotsman

Thanks for the input Bill.

I've now triple checked the hoses coming from under the intake with a gentle tug.............all are attached. Also checked for vacuum at the respective connections, all good.

Tugged on the hose (now will heat the comments) that goes up to the oil filler, all good.

I need a break, going to town to see if I can buy materials to build Dwaynes intake tester.

Calgary Ole

Malcolm, to compare, I have 17.5 HG at 750 RPM. Reving to about 1200 RPM I dipped than reached around 20 HG and my car checked out okay when you helped me out a couple weeks ago and is the same MY.
I am sure you checked but are the two throttle cables too tight and not releasing the TPS?

Snow and rain here tonite!

Calgary Ole

Okay I just read the manual for my vacuum gauge which says "for every 1000' above sea level add 1 HG to the reading". Calgary is about 3500' so 17.5 = 21 HG....Sounds like a leak, but check that your gauge is set for sea level as you are even higher at your home!