Hi, greetings from the far east! I need some advice please. Ok, when I give a really good observe at the vacuum needle on my SARD boost gauge I can see a very slight drifting/revving up and down, which corresponds to the engine sound/speed. Idle fines when loads, i.e aircond, psp etc on so that rules out stepper motor I think. But I do notice that the vacuum needle (not rpm needle) trembles when those loads applied. Is it a case of throttle body needs cleaning or worst intake valves not closing properly? Boost gauge, bov on the way to heaven? Previous owner had HKS adjustable cam gears in but I had them replaced with oem ones and all timing marks checked when new belt was installed. I cannot see any obvious leak somewhere. Would a jumped tooth/timing off cause the described symptoms? Car drives, boosts fine, no spluttering, no white smoke, no stalling at junction or anything of that sort. BTW it's E7 stock with 3 inchers, E8 fpr, E8 fuel pump, E8 actuator. Thank you for reading and sorry for the long essay. Thanks in advance!malaysian ct9a

 

Only means one thing when vacuum gauge fluctuates.

Sticky valves.


Your best test is hook up a vacuum gauge to the intake and snap throttle should shoot up then return down fast. If fluctuates at idle it's sticky valves.

 

oh crap, doesn't sound good. Head job? Thanks for replying Jerry, I'll do as suggested.

 

Hello, Far East! Before ripping your cylinder head off the block you may want to check the throttle body shaft seals and the rubber O-Ring seal on the IAC valve. Throttle body leaks might cause the symptoms which you have described.

So, at least I'd either do a boost leak test of the entire charge air system , or apply some soapy water around the TB shaft ends and the IAC valve with the motor running at idle. At least, it's worth a shot.

 

Jerry, I did what you told me to do. It did shoot up and return down fast but idling still fluctuates a bit.
Hello sparky, thank you for replying! I couldn't see any bubbling / hissing around the areas mentioned when I applied soapy water. I decided to take the TB off and cleaned it with some STP carb cleaner, carefully avoiding the molybdenum coating. Seeing an increase in the RPM I then reset the base idle with MUT-2.
I noticed a gap around the throttle plate when I looked up the sunlight, before and after the cleaning. It got bigger after the cleaning. Would this be the reason for the fluctuating vacuum do you think?

I also have a rattling noise (noisier with A/C on) on idle but dissapear when I dip the clutch. Dunno if its related.

 

Building a DYI boostleak tester is pretty easy and there are several how-to's on these forums. I hope that your problem is not valves.

 

I really hope so too! I'll get the tools and stuffs ready for the tester. Do you reckon the gap I mentioned above is affecting the vacuum?