So...last week, drove to a doctor appointment, and was headed home. Before I got on the freeway, the dashboard lit up like a Christmas tree.



So I pulled to the curb, took a pic, and opened up the owner's manual. Then I called DH, and then I called the shop that had done the 240k service just 3 days previously.

The shop agreed I should have the car towed to them. Happily, I have AAA with a 75 mile towing radius, so the 45 mile tow was free.

We were planning on a trip the next day of 300+ miles, due to a family death and funeral. The next day (Thursday) I got a call to say that the shop had checked out the car, had several leads, but no official diagnosis yet. It was showing two "fuel trim" codes, PO174 and PO101 - too lean. It was also throwing an ECU malfunction code, C1280. They asked if they could keep it for another day or so, and offered to rent us a car for the trip. Nice! We declined, since we had another car we could use. So we did. We headed out to SoCal on Thursday, and left the RX350 with them.

Got back yesterday, and asked for an update. They had been busy! It turns out that they had found a few things, but no "silver bullet" to explain everything. 1) When they reattached a boot/hose coupling, apparently it had folded over on the underside, leaving an air gap. In assessing the issues, they found it, and reattached it properly. The "lean" error codes didn't clear. 2) They also suspected the Mass Airflow Sensor, and replaced it. That didn't clear the codes either. 3) In the end, the shop essentially re-did everything they'd done the previous Friday, and made sure that everything was seated properly. In doing so, and researching possible other issues, they came across the idea of the intake manifold and/or gasket.

So the shop did a smoke test of the intake manifold, and found that it leaked - significantly. Apparently, 240k miles is enough heat and age that the plastic intake manifold becomes brittle...and had cracked along the mold seams. So it was introducing even MORE air to the ICE, and they decided that was the issue. So they sealed up the seams with sealant, and let it harden. They then reinstalled everything, and it apparently worked. Codes stayed cleared, and the Check Engine light stayed off.

So I picked up the car today. Seems to run fine. I asked them to explore the cost of a new intake manifold - which is plastic - and they did. The cost of a new one is estimated at $2300+! Don't think I'll be buying one anytime soon.

So, if anyone has error codes like mine, or a display of codes that include the scary "Check AWD" - know that the CEL and the Check AWD System lights are not necessarily about the transmission....

 

Failed plastic components in the engine bay are a common problem on older high-mileage vehicles these days. I learned that fact from my wife's 2006 Jaguar XK8, now with 118,200 miles. Several of the engine air ducts and hoses are plastic. They sit there in the engine bay and bake through thousands of heat cycles, then eventually crack and split, allowing unmetered air into the system. Some of these cracks can be seen by the human eye, but others can be so tiny that a smoke test may be needed to find them. The moral of the story is this: The fewer plastic components you have in your engine bay, the less likely it is that you will experience these types of issues as your vehicle ages.

 

Under the hood plastics when properly specified (right material) should be able to withstand engine operating temperatures.

Obviously different OEMs use different resins. Older cars obviously did not use the proper resin, hence you may see failures. Not in today's new cars.

 

My experience has been the exact opposite - the significantly older vehicles have the far better plastics. My 1999 Ram's engine bay plastics are holding up quite well. It has the most robust coolant expansion reservoir I have ever owned. The plastic is thick, still flexible, and shows no signs of cracking, unlike the Jaguar reservoirs that after 5 or 6 years will crack if you just brush a tool up against them. I believe that today's engine bay plastic components are much thinner and less durable.

 

I would suggest to check for a used one since there's no rush. I'm a bit worried that those cracks could extend since the expansion coefficient is different. Or did they use some special adhesive?

 

They used a particular epoxy for plastic that is heat-resistant.

Any I agree about searching for a used one; the concern is that a used parts depot would consider this part of the engine assembly, and would therefore be unlikely to offer as a singular part...

ETA: I just googled (which I've been meaning to do since Tuesday), and found an online parts place: TLS Used Auto Parts. They show an upper intake manifold for sale at $135! I will be showing my husband tonight....

 

That sounds great. I've been always under the impression that intake manifolds are not considered to be part of the engine when swapped. I've seen a few from every sort and brand when I used to be a regular visitor of old vehicle yards..

 

What year is this may I ask?

 

2010 per the signature at the bottom of the first post.