Hyundai Forums banner
1 - 6 of 6 Posts

·
Registered
Joined
·
11 Posts
Discussion Starter · #1 ·
2003 Sonata Base (2.4L)
97K
Purchased new August 2003

I have have had rough idle problems for about 35K miles when engine is at operational temp.

When the engine is started from cold it does not idle rough. Rough idle onset is when the engine is up to normal operation temp.

I assume because the PCM is in control mode and is disregarding most sensor inputs, O2, Fuel Tank Pressure etc..

Things I have done:

Tune up including new OE
Plugs, coil packs and wires
New MAF, MAP and Upstream O2 sensor (Monitored Downstream O2 using scan tool as well as bench tested with multimeter and torch checked out fine)

Valve Cover Gasket replaced by dealer (oil leak) under warranty @ 90K

Timing belt, balance belt and water pump done at local garage @ 70K

TPS, EGR, Idle Control all are new and seem to be functioning fine. Sealed off EGR port using gasket material to test if it was the cause, changed nothing, same before and after test.

Smoke tested engine, found one small leak on the Purge Control hose, fixed it no change.

Charcoal emissions filter replaced after tank would not take fuel (apparently canister flooded with fuel) this required fuel tank removal to blow out all the charcoal that clogged the lines from the filter canister, cleaned tank and vent valve as well as tank vent.

I decided to try leaving the gas cap off to see if there was an issue with venting. Drove around several hours, 60 miles or so with multiple engine starts and at no time did it set a gas tank vacuum leak code or illuminate the CEL

I am going to drive without the cap on for a couple of hundred miles to retest.

Tested the Fuel Tank Pressure Sensor, 5V present between supply& ground, 2.5V present when connector is back probed between signal & ground. Signal fluctuates slightly above and below 2.5V when the engine is revved from idle to 2K RPM.

Disconnected FTPS, no code or CEL

Wondering if the PCM is not seeing the signals or possibly failed in that that circuit.

Can disconnect others sensor IAC, Fuel Temp, TPS, MAF, MAP and it will throw the CODE and Light the CEL.

Looking really hard at a PCM partial failure as the culprit.

My scan tool is laptop/software and can read only non-dealer codes i.e. TPS, Short and Long term trim, O2 sensors, engine load and a few others. I can't read the various sensor inputs signals to PCM.

Sorry for the rambling post, but I just hope that I have enough info to get some ideas from the forum.
 

·
Registered
Joined
·
749 Posts
it's gotta see the 'leak' in order to set the code.

it's not going to look for the leak unless multiple conditions are met..

-no other dtc's present: if it sees a fault elsewhere, it may not run the test.
-proper cool down warm up cycles: if you haven't gone through a 'normal' warm up cycle from full cold it may not run the test.
-how much gas in the tank? if its not between 25%-75% it may not run the test.
 

·
Registered
Joined
·
3,041 Posts
2003 Sonata Base (2.4L)
97K
Purchased new August 2003

I have have had rough idle problems for about 35K miles when engine is at operational temp.

When the engine is started from cold it does not idle rough. Rough idle onset is when the engine is up to normal operation temp.

I assume because the PCM is in control mode and is disregarding most sensor inputs, O2, Fuel Tank Pressure etc..

Things I have done:

Tune up including new OE
Plugs, coil packs and wires
New MAF, MAP and Upstream O2 sensor (Monitored Downstream O2 using scan tool as well as bench tested with multimeter and torch checked out fine)

Valve Cover Gasket replaced by dealer (oil leak) under warranty @ 90K

Timing belt, balance belt and water pump done at local garage @ 70K

TPS, EGR, Idle Control all are new and seem to be functioning fine. Sealed off EGR port using gasket material to test if it was the cause, changed nothing, same before and after test.

Smoke tested engine, found one small leak on the Purge Control hose, fixed it no change.

Charcoal emissions filter replaced after tank would not take fuel (apparently canister flooded with fuel) this required fuel tank removal to blow out all the charcoal that clogged the lines from the filter canister, cleaned tank and vent valve as well as tank vent.

I decided to try leaving the gas cap off to see if there was an issue with venting. Drove around several hours, 60 miles or so with multiple engine starts and at no time did it set a gas tank vacuum leak code or illuminate the CEL

I am going to drive without the cap on for a couple of hundred miles to retest.

Tested the Fuel Tank Pressure Sensor, 5V present between supply& ground, 2.5V present when connector is back probed between signal & ground. Signal fluctuates slightly above and below 2.5V when the engine is revved from idle to 2K RPM.

Disconnected FTPS, no code or CEL

Wondering if the PCM is not seeing the signals or possibly failed in that that circuit.

Can disconnect others sensor IAC, Fuel Temp, TPS, MAF, MAP and it will throw the CODE and Light the CEL.

Looking really hard at a PCM partial failure as the culprit.

My scan tool is laptop/software and can read only non-dealer codes i.e. TPS, Short and Long term trim, O2 sensors, engine load and a few others. I can't read the various sensor inputs signals to PCM.

Sorry for the rambling post, but I just hope that I have enough info to get some ideas from the forum.
I know when I have forgotten to tighten the gas cap, it takes a while for the light to come on. Not sure how many miles, but quite a few.
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #4 ·
I will fill up the tank half way and allow cool down and warm up cycles over several days. Maybe the CEL will light this time by following your instructions.

Also I disconnected the Fuel Tank Pressure Sensor today and drove it for a 10 miles, added some gas and the CEL indicated for the FTPS low voltage shortly there after. So the PCM found that fault.

it's gotta see the 'leak' in order to set the code.

it's not going to look for the leak unless multiple conditions are met..

-no other dtc's present: if it sees a fault elsewhere, it may not run the test.
-proper cool down warm up cycles: if you haven't gone through a 'normal' warm up cycle from full cold it may not run the test.
-how much gas in the tank? if its not between 25%-75% it may not run the test.
 

·
Registered
Joined
·
11 Posts
Discussion Starter · #6 ·
I tried the following to test the FTPS.

Back probed ground and signal terminals, then applied light suction to FTPS connector. Key on engine off with voltmeter reading 2.5 Volts dropped to approximately 0.8 volts. Its working or so it seems.

Previous test with FTPS connected and engine running at idle and during revving it never fell below 2.4 volts. I plan to test again tomorrow with tank 3/4 full. If voltage does not drop I will begin chasing at leak again.

Confirmed today that purge valve is pulsing and supplying vacuum.
 
1 - 6 of 6 Posts
Top