1994 Vacuum routing

[MGAJIM]

Gentlemen,
My 94' has developed a serge at idle that quickly got worse. It sounds that a vacuum leak trace is a place to look. Is the main vacuum source at the rear side of the intake manifold? A poor place to get to with much of it hidden, is there any other vacuum locations that may be suspect? A very small diameter white tube at the driver side firewall failed so I imagine there are other plastic/rubber bits that may be falling. Thanks!

 

[Steve83]

No, the only vacuum line that's prone to failure is that white one, for 2 reasons: 1) it's white, so UV passes all the way through it, and degrades it all, and 2) it's near the edge of the hood where sunlight can get in & shine on it frequently.

To check any engine for vacuum leaks at idle, use a mechanic's stethoscope or ~3' of garden hose.

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[motorhead1024]

White vac line to AC/heat blend door is a common failure - sun gets to it thru hood seam - best to replace it. I put a small wire loom over the new vac line to protect it.

Use the diagram on underside of hood to check all your lines - no easy way to get to the vac tree w/engine running - need long arms & small hands!

Good luck!

 

[Steve83]

I replace it with white silicone, which doesn't degrade.

 

[FMOS Racing]

Use the diagram on underside of hood to check all your lines - no easy way to get to the vac tree w/engine running - need long arms & small hands!

Maybe the alien leader from Close Encounters needs a gig?

 

[MGAJIM]

Thank you Gentlemen. I did replace a short length of tube as you indicate with no effect to the idle surging. If I'm reading the Innova 3143 code reader correctly, it shows 63 ( Throttle position sensor to low) and 34 ( EVP-EGR did not respond properly during test). Also I will test fuel pressure and clean the battery terminals just to make sure of good battery current. Thanks guys! You have offered insites in the past that have been much appreciated.

 

[MGAJIM]

Fuel pressure reads 39 psi key on not running and 36 psi with slight fluctuation with cockeyed serge at idle. Next to check the TPS and the EGR unit. I prowled around with Steves suggestion of both the stethoscope and hose piece finding nothing.

 

[FMOS Racing]

If the EGR is stuck open, that's actually a massive vacuum leak.

 

[MGAJIM]

I read that if the IAC (idle air control valve) gets dirty it can also contribute to idle surge. It appears that removing the whole throttle body is the only way to access one of the two IAC retaining screws. Any tips?

 

[MGAJIM]

As FMOS Racing pointed out the EGR was indeed the problem. Small bits of carbon kept it open and was easy to clean. My truck is a 162,000 "daily driver" that doesn't get driven every day. Unlike many guys on this site that seem to modify everything, mine has been just dependable transportation. I appreciate the input from this site to keep it going. Thanks!

 

[FMOS Racing]

My '94 is my daily, gets ~60 miles a day. I'm very happy with the reliability for sure!

 

[Steve83]

If I'm reading the Innova 3143 code reader correctly, it shows...

You can read it any way you like - what matters is that IT does not read codes correctly. You should return it for refund ASAP, and only use the jumper wire method, which never displays spurious codes. Read this page carefully a few times:

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