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Low (3 in. hg) vacuum at idle, slow spooling, loss of power, hard cold starts; BLT performed....

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Gremo87

Proven Member
128
2
Mar 14, 2013
Decatur, Illinois
[Everything I know about the car is in my profile]

Runs on E85 w/Link, speed density, HKS cams (specs unknown), Evo III 16G with noticable shaft play (in/out, side/side, and up/down) and more. Engine rebuilt less than 3500 miles ago. (0.020" overbore)

Symptoms:

- Boost gauge (aftermarket) reads about 3 in. Hg at idle - this is the same value it reads when the car is off. Vacuum will increase while driving, and boost gauge seems accurate - I can still hit 22+psi, but it takes a hell of a lot longer to get there...and just doesn't feel the same.

- Hard cold starts and will die at least twice before warming up a little (125F on gauge) after which it will stay running

- Unstable idle - will go back and forth between stable and unstable, correct RPM and then not (spikes and dips)

- Sometimes while driving it will idle a little high after I've pushed the clutch pedal in when coming to a stop, and then idle will drop to more appropriate RPM after coming to a complete stop.

- Slow spooling (full boost at like 4500+)




I found a couple small leaks with a boost leak test and fixed those - they made no difference. System will hit 25psi and gradually decline from there. I can hear hissing when I open the oil cap during the BLT. I saw someone say that could be the PCV valve. (if not rings or valve seals) I know it's cheap to find out if that's the culprit, but I'm posting here first because I'm low on money. Does this problem scream anything else to anybody?

I have logs, but I haven't completed the checklist for posting logs (don't have timing light yet, haven't done compression test yet, etc). If anyone's interested in seeing a couple just lemme know and I'll throw one up.
 
I have been having the same problem with my GST as well..

- Unstable idle - will go back and forth between stable and unstable, correct RPM and then not (spikes and dips)

- Sometimes while driving it will idle a little high after I've pushed the clutch pedal in when coming to a stop, and then idle will drop to more appropriate RPM after coming to a complete stop.

- Slow spooling (full boost at like 4500+)

i just recently bought mine and off the bat i felt like it was lacking in power ESPECIALLY at rpms lower than 4000....if anybody can help us out that'd be really appreciated..Thanks
 
I'm not sure if this helps, but I had a bad isc/iac on both of my Tsis. On one, I would only get an occasional high idle and I would adjust the BISS to fix it. Eventually I got a CEL, but the IAC still never tested bad.
On the other, I started to get high/ fluctuating idle and wheel hop, and one of the IAC coils tested bad, but no CEL.
I found the upgraded (black) IAC off a stealth for $30 off eBay and noticed a huge improvement.

Also, to the OP I would test or replace your Coolant temp sensor. I had similar issues before replacing mine. And a pcv valve should have been replaced when you did a regular tune up. These two things will cost you $15-20. Also, has the gauge always read the vacuum at -5? It should be -15-20, and at 0 if the car is off. I assume you haven't owned this car for long, so it could be a faulty gauge, or it's not hooked up properly.
 
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I agree with checking that your timing belt hasnt slipped or that your timing is just not flat out off by a tooth or so.
 
Sounds like you should check your timing belt marks still line up, not enough engine vacuum is a result of low compression for one reason or another, or very high lift cam(s).
 
I haven't had a chance to work more on the car this weekend but tomorrow I'm planning to do compression test, check mechanical timing, investigate boost gauge (because as I said it sits dead solid at 3 in.HG both at idle and when the car is off...seems odd to me), and figure out whether my ISC is working correctly or not.

I wish I could say I knew what the vacuum reading was when I bought the car (less than a month ago) but I can't.

Mechanical timing - I haven't been home to check my manuals this weekend and haven't found much in the way of how to check mechanical timing on the internet, but plenty of talk about the whole timing belt process. I understand that the marks on the cam gears are supposed to line up (with piston 1 at TDC) but is there any way to check the lower ones without having to take out the motor mount and jack the engine up?


Also - a new turbo or rebuild is definitely in the future, and I'll look into checking/replacing the coolant temp sensor.

Thanks all~
 
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Sounds like you going off some aftermarket boost gauge or worse based on the factory gauge. Double check with another vacuum gauge before ripping things apart. The lines to after market boost gauges have been know to collapse under vacuum and the factory gauge is based on MAF and load readings driven by the ECU.

DamnSexyMachines feel free to keep reading this thread but open your own thread for your problems. This is Gremo87's thread.
 
Yep I'm going off of an aftermarket boost gauge. The gauge has no problem hitting 15+/- in.hg while driving, but yeah it'd be nice to get a second reading at idle - I'll see if I can rent a vacuum gauge at the parts store later.
 
Also - car dies immediately when I use Link to ground the timing and diagnostic pins. It can handle one or the other being grounded, but not both.

Does that mean anything to anyone?

I'll be working on the car after work today so I'll report back with more info later.
 
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I come with news.

- The ISC seems to be dead. (multimeter displays same thing for all 4 coils - the same thing as when I touch the probes together)

- The plug for the coolant temp sensor appears to have 10v when it should have 4.5 - 4.9.

- Then when I tested resistance at the sensor itself, I get the same thing as when I touch the probes together.

What are the chances of both things I'm testing resistance on being bad and giving the same result as touching the probes together? Is my meter suspect here?
 
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Major Update:

The boost gauge used a vacuum nipple on the throttle body, which sees no vacuum at idle - I T'd it into the FPR line and I now see 14-15 in. HG at idle. When I rev it, it goes up to 20-21. When I hold the engine steady at 3500 RPM, vacuum is at 21 and then spikes to 25 when I let off. (then sinks back to 14-15 at idle)

So is 14-15 at idle ok for a motor with cams? (of unknown lift/duration, unfortunately - just know they're HKS)

It doesn't idle the best, and it's obvious that when the idle is smoothest it's at 15, but wavers...so maybe once the idle is better (tuned..?) it will be making even more vacuum....(?)
 
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