Testing the ICV and boost problem

[chapstic2001]

I have two problems. A nasty idle and no boost.

1. When driving around once the car gets to normal temperature I get a fluctuation in the idle at rest (neutral). Say I come up to a stop light and bring the car out of gear, the idle will go up to 1200 then rest back around 800, then back up and it continues until I drive off. The next light, it will be fine. Does this sound like a faulty ICV? How would I go about testing it? I just brought the car out of storage and haven't noticed it yet. To date I have never seen a car fix itself.

2. Nasty hesitation/buck/lack of boost problem. Again, after the car warms up and I try to spool up the turbo, i get the afore mentioned symptoms. This is a constant problem. I can hear the turbo "wanting" to create boost but it is prematurely venting. Would this be a problem associated with the wastegate? The DV has just been replaced with the new piston style and there are no blatant vaccum leaks.

Any suggestions?

[nynor]

sounds to me like you have a vacuum/boost leak. i know you said there are no blatant leaks, but i am a little skeptical. (don't hurt the messenger . )

i had similar problems. turned out that i had SEVERAL loose hose connections and a split hose under the intake manifold.

also, how old is the intake boot? sometimes they have cracks/splits that are VERY hard to find. check also the rubber connectors on the hard pipes/intercooler.

also, have you checked your fuel pressure/flow at the fuel rail?

one last thing: could be your TPS or AFM.

[chapstic2001]

I would assume that for a boost stumble as bad as it is, a leak would have very noticable...but I wouldn't put it out of the equation my any means. Will double check all hose clamps.

All the vaccum hoses are new and have been replaced within the year. The venturi hoses have been updated with Lindsey hoses. All brand new.

I do not know how old the intake boot is, but I inspected it while I did my engine top end rebuild and there did not appear to be any cracks. It was still soft and flexible.

I will double check the IC hoses.

The TPS is new, 1-year, but the AFM could be part of the problem. How could that be diagnosed?


btw, thank you for the insight.
-Steve

[chapstic2001]

How would I go about checking fuel pressure/flow? Get one of those gauges that connects to the end of the fuel rail?

[nynor]

there is a procedure for checking the afm in clarks garage.

you will need to get a guage that connects to the end of the fuel rail. also be sure to check the flow rate. the procedure may be in clarks garage but is definitely in the shop manual.

[Lawrence Coppari]

The poor idle could be due to the ICV. About all you can do is to insure that it will open and close and is not bound up. One thing that can happen is that the brushes eat the copper ring they contact causing erratic behavior of the unit. The valve is difficult to disassemble. I did it and found what I mentioned above. Can supply a pix if you want. Valve is about 150 bucks so replacing without being sure this is the problem could be wasteful.

About your boost: Have you checked the recirculation valve near the coolant reservoir? It has a nipple on top. Attach a hose to the nipple and apply a vacuum. It should hold a vacuum. If not, replace valve. The valve is held shut by an internal spring as well as positive pressure in the line. So if the diaphragm is leaking, you get no pressure hold. The boost will easily overpower the spring in the valve causing you to lose boost.

[chapstic2001]

Lawrence, If you could email the picts I would appreciate it. Send them to chapstic951@adelphia.net

Regarding the diverter valve, it is brand new from Lindsey. It is the updated version with the piston vs. the old Bosch diaphram model.

[chapstic2001]

Lawrence,
Thank you for the pic. If it starts acting up again, I will take it appart and investigate further.

For the record, a clamp for the IC hose going to the intake was as loose as a 10-year porn star veteran. I the boost still feels weak but is considerably better and I am getting about 15PSI. I am hoping a new wastegate may solve that.

-Steve

[nynor]

15 PSI is well over stock boost settings.

[Zero10]

Yeah, but he's chipped with a boost enhancer. 15psi is about where the stock wastegate shows it's age.

If it feels weak at 15psi I'd be looking at your state of tune (i.e. A/F ratio). 15psi should pin you in your seat if properly tuned.


A loose IC hose clamp is enough to cause your boost problem. Running without hose clamps (don't ask why) I found the hoses opened up at ~2psi.

Is the idle problem any better?

[nynor]

i am trying to figure out how 15 lbs of boost could feel weak... stock boost is only about, what, 9-11 lbs?

[nize]

stock boost with no mods is 12psi with a 15psi spike on initial spoolup.

i had a similar problem in the past which turned out to be the TPS.