Cold Rough Idle & Sweet Smelling Exhaust

Vehicle is 2002 Toyota Tacoma 2.7L 4cyl Engine (3RZ-FE). Recently rebuilt the cylinder head

Okay so I had previously posted a thread on getting random rough idling while driving with some engine codes. That was resolved to be a micro leak in my EGR inlet off the manifold and carbon build up in the intake. Here is the link: https://www.tacomaworld.com/threads/chasing-check-engine-lights.731592/

Now I have a major mystery problem. I’m getting a sweet smell from my exhaust tip, no where else, and a rough idle on start up until the engine is warm. I know this screams engine coolant in the combustion chamber. We know the engine was just rebuilt, so new head gasket. I wanted to know what others think might be the issue. Here is what I've done with coolant system so far; new thermostat, checked the ECT (replaced the copper washer), verified no hose leaks.

Tests I've Completed:
1. Compression test; 170 PSI Across All Four
2. Combustion Leak out of coolant cap (blue fluid test); No Color Change, No Bubbles (was only able to do this for 30 seconds before fluid expanded and started to over flow)

I'm going to complete these items this weekend in hopes of narrowing down issues
1. Burp the Coolant (remove any air in the system)
2. Coolant System Pressure Test (possible crack in engine block?)

 

Coolant pressure test will be the most telling. Was the cylinder head tested for cracks when it was rebuilt?

How much coolant is it consuming? Have you had to top it off yet?

 

Cylinder head was tested by the mechanic who rebuilt the head; confirmed no leaks.

Coolant levels haven't changed but thats primarily because I've only driven it a few miles since I failed my inspection due to EGR issues.

I have a temp sticker now and will be taking it for a longggg drive this weekend and will watch the coolant levels. The burping will ensure I've topped off the coolant properly before doing any driving.

 

You've got it.

Another thing you could check is to let it sit overnight, pull the plugs, and look for moisture in the cylinders with a camera.

When you did the compression test did you leak down test as well?

 

Smell sort of like pancake syrup? That would be coolant.

Depending on how long it’s been since the head was removed, and how much coolant went into the exhaust, you could be smelling what was there before. If you’re not losing coolant, overheating, able to detect exhaust gases in the radiator or anything…..charge hard!!

It will take a while for all of the coolant to burn out of the exhaust, especially if you’ve been driving it easy.

 

Is this assuming coolant is left in the chamber and turned to moisture? I do have some moisture puddling on my exhaust tip (currently using 93 gas) but was told thats normal as fuel tends to have moisture.

I did not do a leak down test, I was under the impression a cylinder compression test and coolant system pressure test would be of equal value to a leak down test (assuming everything passes). Am I wrong?

 

The engine had a horrible amount of that chocolate milk oil and water mixture so I wondered if my catalytic converter is partially clogged, causing a rough idle and a sweet smell...the catch! the previous owner welded the entire exhaust into one solid unit so I hoping its not that!

 

A leak down test would be better for identifying a crack in the head or head gasket issue. That high cylinder pressure will find its way out more quickly in cylinders with a problem. If pressurizing the coolant system is inconclusive it may be worth a shot.


That's correct, if there is coolant leaking into the cylinder over night it would cause a rough idle at startup and excessive white smoke that clears up as it runs.

some moisture in the exhaust is normal

 

Coolant from the engine work that was done in the exhaust system.

See if the smell goes away with a longer road trip

if you have a leak that gets in the exhaust side it tends to look a smoke screen behind the vehicle.

To me the smell of coolant and a bad converter in the exhaust smell nothing alike at all.

 

You may have to drain some coolant out in order to get the combustion gas detector to take more samples. I would do this, as sometimes especially with small leaks, temperature can affect how much it’s leaking… start cold, then warming up, then at operating temperature.
If this test fails to turn your fluid to green, I’d just drive it awhile, and see if the smell goes away. After a completed drive cycle, as described in the service manual, all your readiness monitors are set to ready without a check engine light….or coolant leak, Id say you’re good to go.

 

Tonight I turned the truck on to checking something and a small amount of white smoke is coming out of the exhaust. Which breaks my heart. Worse comes to worse, I'm OK with installing a remanufactured cylinder head rather than using the rebuilt one I have. However I REALLY want to know if there is way to test it's the cylinder head and not the engine block?

 

[RESOLVED] Rough Idle was result of faulty IAC out of the box. I replaced a slew of parts, making it extra difficult to diagnose which part was faulty. Lesson learned, buy any electro/electro-mechanical as OEM. The price sucks but it wasn’t worth the head ache I went through.

The exhaust smell slowly went away as some of you mentioned. Took a good 1000+ miles to make it happen. Having everything tested; coolant compression, cylinder compression, and leak down all gave me peace of mind.