Engine Won't Idle - Need some ideas.

[OwnerCS]

My local Infiniti mechanic replaced the 99 Maxima engine with one from a 95 (rear-ended total) with 73,000 odometer miles (possible). It starts up and runs however we can't get it to idle. It runs fine over 1,000 RPM. When we release the gas, the settles down and dies. We've replaced the MAF with a known good one, installed a new IACV, The EGR was cleaned in the old engine just before installation. New plugs fuel filter and more. We used the fuel rails and injectors from the old engine since they were know to be good before the engine swap.

This new engine has the following (wet) compression readings:

3 cylinders over 142 lbs
1 cylinder at 140
1 cylinder at 110
1 cylinder at 100.

Will these compression readings keep it from idling? It may not idle the smoothest with those compression readings, but would it die?

All the vacuum hoses have been checked.. Vacuum readings appear ok.

Could this be from a bad EGR or fuel pressure regulators?

[Mark Mellott]

Have you checked the throttle position sensor for proper adjustment?

[Mark Mellott]

Yes. A bad EGR or fuel pressure regulator can affect the idle.

[OwnerCS]

The TPS was correctly set before all the trouble started. Though I wonder if I should try another TPS if this one could be the culprit?

It is extremely hard to start when cold. You've got to let it crank for a couple of minutes before it starts up.

[NutriaforBreakfast]

i don't like the compression readings
They should be within 10% of each other
Are the ones that are 100 and 110 close to each other?
If the spark plugs are anything but grey ash I would look closer
at the bottom end of the engine
If you can do a cylinder leak down test on the worst 2 you
might figure out where the problems are (oil rings, head gasket, etc)

[OwnerCS]

Thanks Nutria - The shop is going to run a leak down test.. The engine sat in the wrecked car for several months before I got it.. The car was rear ended.. I've had a larger variance on the I30 that settled down after I started driving the car on a regular basis. I think the issue may be from the valves sitting in an open position for several months that need some time to reseat -- hopefully.. The idle issue started on the existing motor right after it jumped timing.. We moved the injector rails, intake plenum, TPS, EGR and all from the 99 model engine to the 95 model that has been installed. I just replaced the IACV on Friday (no luck) then I dropped off a new fuel pressure regulator at the shop today.

It's a really nice 5-speed 99 model with great suspension, interior, and body..But the whole idle issue is making me crazy and sick all at the same time..

[NutriaforBreakfast]

With the leakdown test if the exhaust valve is open, air should exit the exhaust pipe
If the intake valve is open, it think you can open the oil filler cap and hear air there
If the headgasket is bad, you should see bubbles in the coolant
I really have never done on though

[the converted]

That's pretty much it. Noise from the oil fill is either going to be rings or a bad HG, bubbles in the coolant is a bad HG. Most of my experience comes from race cars where we'd pull the engine if leak down got past 15%, but I think for a street car I'd guess anything up to 25 or 30 should be OK.

The other question I have is what do the plugs look like? If they are covered in oil, it's always going to be a pain to start and definitely points to bad rings. Those compression numbers do look a little sketchy to me.

[OwnerCS]

The plugs all looked good. No indication of oil burning or any difference in firing between cylinders. We had the oil pan off and checked out the tensioner and cam shafts. The engine had been well maintained by the previous owner it appears. After the car was in the wreck, someone removed the left hand (front) fuel rail and coil packs. The car must have sat in the elements for sometime with the fuel rail removed. The low cylinders are also on the front left hand bank. I suspect the valves from that bank were exposed to the elements without the fuel rails and some rust or corrosion developed on the valves. I want to drive the car for a couple of weeks then check compression again. Hopefully the valves will spin and seat after some driving time.

[NutriaforBreakfast]

i dont see how you could have good vacuum gauge readings with low compression on 2 cylinders

[OwnerCS]

After driving it for a couple of weeks, it has settled down now idles good. I think the valves needed to settle in after the engine had been sitting with the fuel rail removed. I'll check the compression in a few weeks. It seems to have more power than the old engine ever had. It runs like the first Maxima - 95 5-speed.

[NutriaforBreakfast]

I live close to Dallas. There is one that's been sitting for 2 yr now.
Body outside in good-interior is far. Tires and wheels look ok.