# Backfire through intake manifold-warm up problem consists after changing many parts



## jmaggrahpics (Apr 4, 2013)

Hey everyone. 

Long story short short. I had a fuel distributor that was tuned to rich. Instead of tuning and messing with it I bought a used one off a running cabriolet. I've replaced all of the following parts with used ones. Fuel pressure warm up regulator. Cold start valve. Idle valve (behind intake manifold) frequency valve both fuel pumps all relays fuel distributor 


Yet this problem still consists. The problem is that when I start the car it does first time. Then starts. Idles great but when I go to rev it. It bogs and backfires through the intake manifold. Until it's been running for a couple mins. After that it runs and revs great. But that's with the 02 sensor un plugged. With the 02 sensor plugged in. It wot revv at all 

With the other distributor. It ran so rich that it blew black smoke. An didn't idle.. But revved when cold but not well (still struggled until warm) 

Changed the o2 sensor and it cleared up some of the warm up issues. But once warm it won't rev unless the o2 sensor is unplugged 


What else could it be?

FYI first time posting in this forum 


Vacuum leak ?
Bad used part that I replaced ?
Clogged cat?
Clogged accumulator or fuel system component? I doubt it cause it runs good warm..

Any thoughts? So close guys.


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## Zhorik (Feb 9, 2014)

Ignition?


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## jmaggrahpics (Apr 4, 2013)

Yes cis lambda 

1987 cabriolet 


1.8 L


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## Zhorik (Feb 9, 2014)

I meant maybe ingnition was set earlier\later.Even if the plug is connected doesnt mean that ignition apply works :sly:


Я.R


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## sc3283 (Dec 23, 2014)

injector O rings or injector plastic inserts leaking(sucking air) or broken...both quite common on CIS.

Squirt carb cleaner all around each injector ....if O ring or plastic inserts are broken...idle quality will change

both rubber boots and plastic air tube are good?

have you adjusted the mixture properly(setting plate height)


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## rabbitnothopper (Oct 19, 2009)

start with fuel pressure...

get the $50 kit and start testing
http://forums.vwvortex.com/showthread.php?6060634-DIY-Fuel-Pressure-Tester


next get a dwell or duty cycle meter and check your o2 measurement
the test port is near the passenger strut tower


ok got those set properly?....

now check for vacuum leaks and correspondingly adjust the fuel/air ratio again while reading both fuel pressure and dwell


great!
anything else would be spark or fuel injector.


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