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Slow drop to idle, Poor throttle response. But still preforms desent.

 
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  #1 (permalink)  
Old 14 Jul 2013, 04:09 pm
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Default Slow drop to idle, Poor throttle response. But still preforms desent.

Hi.

I'm trying to bring back the pleasure of driving my sisters PT Cruiser.

The problem has been there some time. But there has not been time to make some deep search for the actual fault or any competent garage to fix it.

This is how it currently preforms.
Starts ok, Idle no problem, Steady state low speed or high speed no problem.
Slow acceleration and deceleration no problems. (including cruise control )
MPG is reasonable.

City driving sucks. Since the engine has a somewhat slow drop of rpm and once back on throttle the response is rough. (I.E. Gear Change, Stop at intersection)

At speed 50ish with increasing throttle or overtaking does not obviously present any problems. Same thing with lower speeds an higher rpm. Increasing throttle at a high rate does work fairly ok. I'm not that familiar with how good or bad this car should preform.

At all situations the ECU can be assumed to be running closed loop lambda control it works fine. Idle control also does its work fine.
At open loop such as acceleration there must be some faulty input or state that causes the ECU (PCM) to act in an undesired way.
Have not confirmed this with a wide range lambda logger.

There are no DTC codes active.

Fuel delivery and fuel pressure. Low pressure or flow could affect situations such where a lot of fuel is needed. Low rpm high torque situations. But to me it's not really a obvious fit into the symptoms of slow drop of RPM problem.

TPS an wires. A potential fault source. Will make a measurement of that signals just have to get the Scope to make some a sweep.

MAP sensor. Can get that it would have larger impacts at an on throttle situation. But could it also affect the off throttle situations. Have read that this sensors is a variable resistance type sensor. Is it that simple that it also could be measured ? I was expecting something semi active with at least a buffered output.

Intake leaks have been searched for both visual and with starter fluid. O rings where fresh an located where you would expect them to be.

Timings sensors. I would have expected more problems at other situations as well. A long long shot. Would be some ground or supply faults related to the fact injectors running high duty cycles.

Plugs and Wires i have checked. They where fresh and reasonable resistance in all of them. No obvious rich or lean condition on any visible from spark plugs.

My sister had the car to a dealership/garage for this problem. They just claimed it to be Plugs and Wires that they changed once more. A worthless overpriced low quality work... Made no difference what so ever except $$ and a discharged battery. Was replaced as winter arrived.

So whats your advise ?
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Old 14 Jul 2013, 05:12 pm
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Default Re: Slow drop to idle, Poor throttle response. But still preforms desent.

After reading all that, all I get out of it is there's a slow drop in RPM's when you let off the throttle and when you get on it, the response is rough.

The TPS as you mentioned (and haven't measured) could have a lot to do it with the RPM drop along with a good cleaning of the throttle body itself. I don't believe the TPS is serviceable just replaceable.

The roughness of the engine could be, as you mentioned, low fuel pressure or partly clogged injector(s), dirty (clogged) air filter or a faulty/dirty IAT (Intake Air Temperature sensor.
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Old 15 Jul 2013, 03:41 pm
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Default Re: Slow drop to idle, Poor throttle response. But still preforms desent.

Quote:
Originally Posted by CREWZIN View Post
After reading all that, all I get out of it is there's a slow drop in RPM's when you let off the throttle and when you get on it, the response is rough.

The TPS as you mentioned (and haven't measured) could have a lot to do it with the RPM drop along with a good cleaning of the throttle body itself. I don't believe the TPS is serviceable just replaceable.

The roughness of the engine could be, as you mentioned, low fuel pressure or partly clogged injector(s), dirty (clogged) air filter or a faulty/dirty IAT (Intake Air Temperature sensor.
Nice to read that your ideas are partly similar to mine.

TPS agreed. Working on that.

IAT I would not have contributed such a large impact on that sensor at all occasions. But why not.
Lets say the sensor reading detect to cold temperature and hence a indication for a rich mixture. That perhaps cold be neutralized/reversed by lambda inputs on steady state operations but not others. I would however expected some difference in how it acts when cold or warm outside.

I would have expected a faulty MAP reading to have a greater impact. Specially since its that type of sensor that usually has low diagnostic coverage and DTCs.

Im currently trying to source some parts locally.. If i do find them at reasonable prices. Will get back with my findings.
/ Johan
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Old 22 Jul 2013, 03:00 pm
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Default Re: Slow drop to idle, Poor throttle response. But still preforms desent.

Have had some time in the garage.

TPS was all fine. Found no measurable faults.

IAT that NTC resistor is there connected and changes Resistance vs temperature. At 68F 18C ~13kOhm with some gentle heat resistance dropped. Did not find any table for resistance.

MAP did nothing with it as had no good test. A small mark on the Oring seal, so it was replaced. Mainly a preventive action.

ICV did have a lot of carbon build up. But it was not stuck. Did try an measure on in and belive i could have found two coils at ~52 Ohm.
What really made me concerned was the alignment of the piston vs housing. It appears to hit the wall to some extent rater then the seat. I assumed there must have been some type of bearing inside the ICV completely worn out.

Plugs , Wires had them all removed and measures. All on spec but one spark plug that was a bit darker then the rest of them. Turned out to be some type of oxidation at the coil pack side of that wire.

Battery voltage was also on low side. Has been standing a bit to much without maintenance charging. Battery was recharged with a Ctek changer to make sure no impact form voltage. Since i have heard form a few PT owners the cruiser are somehow sensitive to low voltage.

Final result at test drive.

Throttle response - OK
Idle - Ok better then before.
Throttle lift of. - Somewhat both good and bad. Greatly improved but not ok. A new IAC will most likely cure this.

Keep on cruising

/ Johan

Last edited by JohanL; 22 Jul 2013 at 03:02 pm.
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Old 22 Jul 2013, 04:01 pm
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Location: Bexleyheath, Kent, UK
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Default Re: Slow drop to idle, Poor throttle response. But still preforms desent.

Hi Johan

I am a little confused, you seem not to have done anything but check items and yet your test drive says there is an improvement. I am interested as I have the same issue of rpm dropping slowly although acceleration is OK, although I do have a loud possibly pinging sound (sounds like marbles rattling in a tin) on hard acceleration which I am trying to sort.

Tony
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Old 22 Jul 2013, 04:02 pm
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Default Re: Slow drop to idle, Poor throttle response. But still preforms desent.

Forgot the picture of the idle control valve seat.
Attached Images
File Type: jpg PTidleW.jpg (60.8 KB, 78 views)
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Old 22 Jul 2013, 04:19 pm
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Default Re: Slow drop to idle, Poor throttle response. But still preforms desent.

Quote:
Originally Posted by Jassy View Post
Hi Johan

I am a little confused, you seem not to have done anything but check items and yet your test drive says there is an improvement. I am interested as I have the same issue of rpm dropping slowly although acceleration is OK, although I do have a loud possibly pinging sound (sounds like marbles rattling in a tin) on hard acceleration which I am trying to sort.

Tony
Sorry. Was perhaps a bit unclear. Just wanted to highlight my located issues.

- One semi faulty connection on a spark plug cable. At connection to coil pack. Most likely weak spark since okej at light load but not at high load.

- Idle Contol Valve. Most likely partly stuck due to carb/oil buildup and some kind o internal to IVC wear that created misalignment between seat and icv piston.

I did remove the entire air intake with all the sensors and actuators. To check for air leaks or faulty sensors.

All seals and vacuum hoses where fine. Then i measured sensor by sensor as far as i could do. Then only sensor i could not cover in any good way was the MAP sensor. Cleaned all as well as possible.

When all was measured and cleaned. Reassembled and did the test drove. With the result that full load problem was gone (spark plug wire problem). The rpm drop issue was partly still there. Due to the fact i was not able to replace the ICV valve. just bring it partly back to life. Will order a new one an my assumption is that problem will be gone by doing that.

Last edited by JohanL; 22 Jul 2013 at 04:22 pm.
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Old 22 Jul 2013, 04:46 pm
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Default Re: Slow drop to idle, Poor throttle response. But still preforms desent.

I am having same problem with mine if anyone can help
when I dip the clutch to change gear the revs drop fast to 1500 then seem to take a good few seconds to drop the rest of the way
so if you change gear fast the revs don't drop of and it does not give a smooth gear change

I have taken the throttle body off and gave a good clean but no dif at all
please help
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Old 22 Jul 2013, 05:34 pm
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Default Re: Slow drop to idle, Poor throttle response. But still preforms desent.

Quote:
Originally Posted by JohanL View Post
- Idle Contol Valve. Most likely partly stuck due to carb/oil buildup and some kind o internal to IVC wear that created misalignment between seat and icv piston.

Forgot the picture of the idle control valve seat.

the IAC has no bearing in it. the cup moves in and out on a screw style post. the
clean spot you see is likely from the airflow path through the valve. this is why it
is clean there, not shiny.


my car also takes too long to return to a low idle, but i believe the problem to be software
related. it only happens when the AC is on and the ECU raises the idle to compensate.


this drove me nuts last year, i like downshifting and it does not slow as fast with the AC
on. i ended up unplugging the IAC for the summer.


i have replaced the IAC for the Idle issue you are describing, and i can assure you
that replacing it will make NO difference.

Last edited by rob342; 22 Jul 2013 at 05:52 pm.
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Old 23 Jul 2013, 02:34 am
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Default Re: Slow drop to idle, Poor throttle response. But still preforms desent.

Quote:
Originally Posted by rob342 View Post
the IAC has no bearing in it. the cup moves in and out on a screw style post. the
clean spot you see is likely from the airflow path through the valve. this is why it
is clean there, not shiny.


my car also takes too long to return to a low idle, but i believe the problem to be software
related. it only happens when the AC is on and the ECU raises the idle to compensate.


this drove me nuts last year, i like downshifting and it does not slow as fast with the AC
on. i ended up unplugging the IAC for the summer.


i have replaced the IAC for the Idle issue you are describing, and i can assure you
that replacing it will make NO difference.
Have to both agree and disagree.

This car i have been working on has the -01 to -02 2.0 style of ICV. The piston part is a metal cone shaped thing. If I have understood it correctly this version was replaced by a larger diameter "rubber" cylinder thing on other years and engines.

In my case there are definitely some wear one that piston and not the seat. Making the shape of the piston not a perfect fit for the seat. And can not seal properly as it once could have done. Magnitude of this imperfection i have no experience of making a accurate judgement on.

Hence i will replace it for peace of mind. But you (rob) may still have the right experience. I could be wasting money.
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