Looking for Advice on P1172 and P1175 Codes
 

So, I'd like to know what all I should consider checking with these two codes.


I know they typically refer to the MAF sensor, but I've tried several different MAF and still getting the same cold start issues.


I've checked all vacuum related lines. Cruise works great. Nothing odd aside from a nipple on the passenger side of the plenum that has no hose attached. It's right below the other two vacuum hoses that connect to the top of the plenum. Year is a 99.


My intuition is leading me to believe it may be the injectors or injector seals. Is that possible with these two codes? I think it could be the injectors because I believe there is a loss of air somewhere in the vacuum system which is causing the rough idle on cold starts.


Otherwise everything is great after about 1500 recent miles. Once started and warmed up, she runs quiet and cool.


Just need some assistance pinpointing the vacuum codes.


Thanks for any help.

I would start it up cold and pour some water along both sides of the lower intake manifold. Leaking intake gaskets is a pretty common problem on lots of vehicles. If it's leaking, you'll hear it sucking in the water.
If it doesn't suck in water, it's possible that your IAC valve isn't working correctly.
Also, if your coolant temp sensor is giving an incorrect temperature, that can also cause rough running at certain engine temps.

I will try the water hose method. Wouldn't I get the same effect by spraying starting fluid around the intake gaskets and be able to diagnose that as the problem if the rpms increase?


I recently cleaned the IACV, but there is still visible carbon deposits. If I could dismantle the iacv, I feel like I could get it completely clean, but the scrrews that hold the assembly together have epoxy over them. I may have to buy a new one.


I guess I will try that before digging into the injectors. I wish I had checked the injector seals when I changed the plug wires, but I didn't want to create a new problem.
Thanks for the suggestions.

Usually a good idea to search for & look at the LR code description versus generic in the manual. Doubt IACV or intake leaking causing a rich condition.

From injectors section:
......

I also see a rich system can cause an O2 sensor to throw a code. I have been thinking my problem could possibly be clogged cats. Maybe that mixed with injector seals or bad injectors. It's just my guess based on the mileage and some recent hard driving after mostly being used for day to day short commutes.

Oh wait a minute, I misread your post. I read vacuum leaks, rough running on startup and I didn't pay attention to the codes in the heading. I apologize for that.
No you don't have vacuum leaks, or at least that's not your problem.
I would check out the coolant temp sensor. If the maf is good and it runs good when warmed up. Connect a scan tool and watch the coolant temp from cold start all the way through warm up. I usually graph the reading so if it drops out or changes erratically you'll see it.

No problem. I will switch to graph. That's a good idea.


So far, the temp gauge doesn't have any wild swings, and it levels off to about 194f once warmed up.

It's just one possible cause of temp specific problems.


You could always try unplugging the maf on a cold start an see if it runs better.
I don't think clogged cats would be the problem. I would think that would make it run poorly at any temperature. Not that I would rule it out completely without looking into it further. But I would start with fuel and air first.


What do the fuel trims do as the engine warms up? Do they start going back towards zero?


Also, don't forget the intake air temp. That can sometimes cause some trouble too if it's not accurate. I would go through all the data pids while the engine is cold and see if anything looks out of place.

So, I started digging around. Checked oil breather hoses, noticed I didn't latch the air filter box last time I was in there, and then noticed an oil leak.


The oil leak led to further inspection and I noticed the flywheel plugs are no longer there. Couldn't tell you how long it's been like that.


Now I have a lot of cleaning to do and have to figure out a substitute for the plugs until I can buy them from a local parts store or order new ones.


I will continue to update as I diagnose and fix.

It's only one flywheel plug missing. Thought the other was gone, but it's still intact.


I think I will do an induction cleaning and engine oil clean. Then plan to drop the oil pan, clean out any grime and replace the oil pan seal.