Intermittent Idle issues - Vacuum lines

In a previous post, I mentioned that the engine had an intermittent idle. When running at operating temperature, it would skip a beat and would sometimes surge. The tach needle would not stabilize or stand still.

As mentioned earlier, there are four potential contributors that could cause this idle.

• The fueling delivery system was original and there could be clogged injectors. 
• The numerous bare wires could be causing electrical issues
• The worn spark plug wire 
• Numerous vacuum leaks

I decided to explore each of the possibilities and address each individually. When I inspected the vacuum lines, I never got too deep into the multitude of vacuum hoses present on the PG motor. The digifant engine management is notoriously vulnerable to vacuum leaks. I checked the most common areas including the screw on the bottom of the throttle body. These seemed to be okay.

However, looking more closely at the firewall exposed some very worn vacuum hoses. I'm quite positive there are leaks. So I opted to replace all of the lines.

1 meter ECU Vacuum line

There is one important vacuum line from the throttle body to the ECU. This is a special hose that has to be exactly 1 meter in length. So I went to the dealer to purchase an exact replacement at the correct length. If this is so sensitive to length, I would imagine it would also be sensitive to internal volume. So I went to the dealership and purchase the correct length replacement with an exact replacement. Cost was roughly $26 for the meter length of hose. The existing hose was used as a reference. There were no clamps on the original. So I left it that way.

Germanautoparts has a Corrado G60 vacuum hose replacement kit. It contains all of the necessary lengths and internal widths.  The individual pieces are pre-cut. My thought is the kit would allow me to quickly identify which lines should be replaced and it would also give me confidence that I've identified all of the critical vacuum lines. But this kit was always sold out. No surprise considering that most corrado owners are probably trying to solve the very same issues. With the kit unavailable in the near future, I decided to see what others were doing.

I found a couple of discussions on the online forums outlining all of the different sizes and length necessary to replace the lines. However finding some of the unusual metric sizes outside of the dealer was proving a challenge.

After doing a few unsuccessful searches online, I decided simply to take a sample with me to the local autoparts store and get 20 feet of something in similar size. The hard to reach lines were clamped with crimp on style clamps. These were difficult to extract so I simply cut them out ensuring to leave sufficient amount of the source to attach the new lines when replaced. There are also numerous T & Y shaped fittings up near the coil behind the intake manifold. Some of these were also encased inside shrink tubing. There too I simply cut them out making reference so that I could fit the proper length while replacing.

I bought 6mm clamps in bulk but sadly they did not fit the outside diameter of the SAE hoses. Despite the lack of clamps,  the hoses seem to grip the barb fittings tightly, furthermore some of the existing hoses also did not have clamps so I don't believe they are a necessity.  Every fabric braided vacuum hose I could find,  I replaced with the fresh rubber vacuum lines. Lastly, to replace the protective vinyl exterior jackets that encased the original hoses, I substituted plastic wiring loom.

I was especially careful with plastic fittings. These are old and brittle but if I break them it will be difficult to replace. So I exercised care to delicately extract the old hoses--sometimes using a xacto blade to cut them off.

If I encounter a leak during operation or the hoses blow off, then I'll invest in clamps. But for now, I'm happy to have replaced all of the suspect vacuum lines, routing them properly in an orderly and best fit arrangement. And lastly, I encased them in plastic wiring loom to protect them against the harsh environment underneath the hood and to make some semblance of order in the engine bay.

By doing this I've made a thorough effort to remove vacuum leaks--one of the most common culprits in rough engine idle.  That's one less thing to worry about.