99' Saturn SL2, DOHC; Plastic fuel rail, alum TB
Car is idling a little rough. My concern is hooking up a vacuum gauge on idle it bounces about 3 units{ inHg? } in range of 19-17. Shifting to drive drops the vacuum a few units and about the same bouncing, if not worse. Is my gauge just too sensitive or am I to assume there is a problem? ( I don't think I have any problems I notice other that rattling car. Codes all cleared after fuel injectors and testing the purge valve )

Below is what was done to it before now. the biggest problem being fuel delivery was minimal because of bad injectors

The vacuum gauge showed much worse before some replacement parts. It was surging ( doesn't surge anymore ) and more of a bounce, especially in drive. It would die if coming off the highway and [size=13px]stopping[/size] at a light.

I already did a smoke test
- tests were inconclusive. Saw smoke at the TBI, but couldn't tell where on the TB. Could be from the plastic intake that hooks to the front of the TB, the butterfly valve. I did spray carb cleaner all over it while idling later, and found no leaks.

Replaced the EGR ( didn't figure out how to test this one, but I hear it's a sensitive device so I probably killed it a while back )
Replaced downstream && upstream O2 sensors{ bad };

Tested for backpressure, hoping my CAT was clogged. Hooked up a gauge to the upstream O2 sensor location, ran the car and had no vacuum/back-pressure. To verify results, I clogged the muffler, got a reading on the gauge.

I wish I could tell you what codes I had before, but I don't think it matters as I was riding with bad parts for too many years, spark plugs too. Even before the rebuild after head gasket failure. Got some nice COPPER NGKs in now.

MAP also replaced ( had a code, I think ).
Finally, I thought to look at the fuel system. Took the spark plugs out and tried backflowing some cleaner through them. Obvious problems with flow. Replaced them all and new 80? usd fuel filter. This fixed the idle surging. and now I'm still left with the rough(?) idle.

I know timing could be a thing, but I don't see that being a problem as it was just rebuilt, by me. Verified the timing marks more than a few times ( during install ). Will say I was a little scarred the new chain was too loose, but one bump of the key in ignition fixed that.

Thoughts? Anyone run a vacuum gauge or can think of something I need to check out?
Oh, I thought maybe the purge valve was bad since it might(?) cause idling issues, but I couldn't blow through the thing when removed. And applying 12V I was able to blow through it. So it at least functions. I re-installed it, Ohms across the terminals was 29V.

Fuel pressure seemed good after injector/filter install: I did fuel pressure test at shrader valve on fuel rail. 60psi on idle, shutting down immediately drops to 46psi. An hour later, it dropped down to 42psi. Feels good to have good fuel delivery. Also noticed it was shifting smoother and vacuum gauge seemed more responsive to shifting gears ( auto tranny )

 

Yikes.

What RPM does it idle at when warmed up?
Does this RPM waver? What's the spread?

Spray throttle body cleaner all the way around each of the runners of the intake manifold where they meet the head. If the iidle increases by ear when you are spraying, you likely have an intake manifold vac leak. I have to go look up what the quivering vacuum reading is indicative of. Can't remember.

 

What's the compression in each cylinder after the rebuild?

 

The idle hasn't been a problem. It sits at about 900, maybe 8, no less. No waver of rpms, so no spread. The spread on the vacuum was listed. THough, warmed up let's say 17-15 in-Hg spread.

That would have been a great test to run right after the rebuild. I'll look for my compression gauge or rent one soon {tomorrow?}. I don't suspect problems with the bottom/top, but there's no reason not to test, if anything for numbers to compare later down the road.

Also, I really tried to spray everywhere, on the intake. Only thing I didn't do was get under the car to get good sprays underneath the runners. You're not going to go and tell me it'd be a good idea to spray from underneath are ya ?

 

That vehicle should be idling at 750 ish. Need to go look it up. I'm thinking possible vac leak leak or other issue with air seeping in when it shouldn't. A vac leak is not inconsistent with the wavering vac results but there are other possibilities, so don't go out and throw parts at it.

You can get most of the other side of the runners from the passenger side by contorting your arm around the power steering pump. Not pleasant but it gets the job done