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Technical RPMs rise up when gas pedal is released

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Technical RPMs rise up when gas pedal is released

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sgorchichko

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After throttle cleaning I noticed that when I'm going to change the gear and I'm releasing the gas pedal and pressing the clutch pedal the RPMs are rising up for about 300RPM.

What should I look for?
 
sgorchichko said:
After throttle cleaning I noticed that when I'm going to change the gear and I'm releasing the gas pedal and pressing the clutch pedal the RPMs are rising up for about 300RPM.

What should I look for?
Click to expand...

Did it do similar stuff before the clean? Are all the connectors OK on the throttle (e.g. TPS, MAP, etc)? How exactly did you perform the cleaning? (on car? off car? meaning, did you take throttle body off the inlet?)

If it is MAP engine, it might be some air leak somewhere, as when you get extra air into inlet manifold (e.g. vacuum leak), MAP engine will start adding fuel. Does it bounce revs on idle?

Do you have OBD scanner with possibility to check live data? I would consider checking fuel trims.
 
igno said:
Did it do similar stuff before the clean?
Click to expand...
No. Just RPMs jumping on idle from 500 to 1000.

igno said:
Are all the connectors OK on the throttle (e.g. TPS, MAP, etc)?
Click to expand...
They seems to be OK. How can I diagnose them?

igno said:
How exactly did you perform the cleaning? (on car? off car? meaning, did you take throttle body off the inlet?)
Click to expand...
The throttle body was removed from the engine. Cleaned using carb cleaning spray and installed back. After that I performed the throttle learning procedure rising the RPMs to 4-5K three times.

igno said:
If it is MAP engine, it might be some air leak somewhere, as when you get extra air into inlet manifold (e.g. vacuum leak), MAP engine will start adding fuel.
Click to expand...
I'm thinking about air leak, too.

igno said:
Does it bounce revs on idle?
Click to expand...
No now. The RPMs on idle are pretty stable, about 800 +- 20 RPMs.

igno said:
Do you have OBD scanner with possibility to check live data? I would consider checking fuel trims.
Click to expand...
Yes, I have. Could you tell me what parameters should I track?
 
sgorchichko said:
No. Just RPMs jumping on idle from 500 to 1000.
Click to expand...

RPMs jumping +-500 sounds like an air leak, TPS, MAP, etc, etc. But surely not normal.

sgorchichko said:
They seems to be OK. How can I diagnose them?
Click to expand...

Well, I would unplug each, check if it has any wiring issues (loose wires), if pins have any corrosion, if something was not fully plugged, etc ...

sgorchichko said:
The throttle body was removed from the engine. Cleaned using carb cleaning spray and installed back. After that I performed the throttle learning procedure rising the RPMs to 4-5K three times.

I'm thinking about air leak, too.
Click to expand...

You can test for air leaks either with propane or water. I would prefer water for safety concerns. Spray water around the suspected places (throttle connection to manifold in this case) and see/hear if water gets sucked in.

sgorchichko said:
No now. The RPMs on idle are pretty stable, about 800 +- 20 RPMs.
Click to expand...

Not sure what is "desired idle" for stilo, but fluctuation of +- 20 sounds totally normal to me.

sgorchichko said:
Yes, I have. Could you tell me what parameters should I track?
Click to expand...

In this case I would first go for fuel trims. Those are usually the key to vacuum leaks analysis. If it is 100% MAP engine (I haven't seen stilo engine myself, so just guessing here), it would be adding extra fuel if it has extra air in the manifold. Thus, what you would observe is Short Term fuel trim (aka "Integrator" in Fiat terms) starting to increase and later on getting compensated with Long term fuel trim (Block Learn in Fiat terms). In "perfectly working car", LT should be 0 (or 128, if they take it 0 to 255) and ST bouncing around 0 (going a bit over it and then jumping below 0, and over 0 again and so forth). You can also take a look at lambda readings ... But just to make sure that lambda is working fine (unfortunately, these days lambdas play too big of a role in engine performance), but let it warm up first as lambda needs around 600C to function properly (ECU should say that it is in "closed loop" when it starts to take lambda into account).

Also, you can see what MAP sensor is reporting (inlet manifold pressure) and, what TPS is saying when you press gas pedal and release it.

Something like that for a start ...
 
igno said:
In this case I would first go for fuel trims. Those are usually the key to vacuum leaks analysis. If it is 100% MAP engine (I haven't seen stilo engine myself, so just guessing here), it would be adding extra fuel if it has extra air in the manifold. Thus, what you would observe is Short Term fuel trim (aka "Integrator" in Fiat terms) starting to increase and later on getting compensated with Long term fuel trim (Block Learn in Fiat terms). In "perfectly working car", LT should be 0 (or 128, if they take it 0 to 255) and ST bouncing around 0 (going a bit over it and then jumping below 0, and over 0 again and so forth). You can also take a look at lambda readings ... But just to make sure that lambda is working fine (unfortunately, these days lambdas play too big of a role in engine performance), but let it warm up first as lambda needs around 600C to function properly (ECU should say that it is in "closed loop" when it starts to take lambda into account).
Click to expand...



This is how terms are working:
 
Last edited:
This is the graph from Ecuscan.
 

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sgorchichko said:
Any ideas, guys?
Click to expand...
Hi,
Sorry for the time it has taken to reply, unfortunately life strikes sometimes. :)
Anyhow, lambdas are a bit off, as pre-cat lambda should circulate around 0 point. However, that is not to be concerned. I would start looking for a vacuum leak. Unless you have done it many times before, I wouldn't recommend going for fuel source based test (spraying break clean or something similar on manifold), due to safety concerns, but rather spray water and listen for it to be sucked in. Unfortunately, the fuel trim video is not available any more, could you re-upload it once again, meanwhile trying water test?
 
sgorchichko said:
I shared the YouTube video for everyone. Hope it helps.
Click to expand...

OK, well, if the situation on the video is during idle ... You can see that short term (red line) is constantly up, barely reaching 0 when long term is compensating. As said before, I'm not exactly sure of how this particular engine is, but if it is a MAP engine (which I tend to believe it is), then it might be a classical case of vacuum leak, as MAP engine will compensate a vacuum leak by adding fuel, as the intake pressure will change. As in any other case, the vacuum leak is affecting mainly idle performance, as on WOT (wide open throttle) it wouldn't affect as much. So, I would start looking for vacuum leak.
Another thing is "Does it have IAC (idle air control) valve"? If yes, what is the value of that on OBD? Is it fully closed?
 
sgorchichko said:
I shared the YouTube video for everyone. Hope it helps.
Click to expand...

One more thing, please check if it is a MAP or MAF engine as reading the behavior is quite different when it comes to how fuel trims are behaving in different situations.
 
igno said:
One more thing, please check if it is a MAP or MAF engine as reading the behavior is quite different when it comes to how fuel trims are behaving in different situations.
Click to expand...
looks like Stilo's 1.6 has only MAP sensor.
 
igno said:
Another thing is "Does it have IAC (idle air control) valve"? If yes, what is the value of that on OBD? Is it fully closed?
Click to expand...

As far as I know the Idle Air flow on Stilo's is controlled by a throttle.
 
OK, assuming that throttle is nice and clean, judging from previous posts and butterfly is not sticking, I would again suggest a vacuum leak test. There are 2 rather different types of vacuum leak. If it is only misbehaving at cold and gets better when engine is warm, it is likely intake manifold gasket leak (motivation: When engine warms up, metal and gasket are expanding and close down the leak). If it is the same on both cold and warm, it is likely a leak in a manifold or somewhere else.
As said, take a spray bottle full of water, run the engine and listen for it to start sucking the water in. In some cases, it might affect the idle as well when water gets into cylinders. One word of advice, if there is a severe leak somewhere, don't drop too much water, as you are risking flooding the engine and getting it hydrolocked (pro mechanics say that there is no risk of that, but I would be careful). Another way is to use propane, but it is a dangerous thing, so I don't recommend that way.
 
igno said:
OK, assuming that throttle is nice and clean, judging from previous posts and butterfly is not sticking, I would again suggest a vacuum leak test. There are 2 rather different types of vacuum leak. If it is only misbehaving at cold and gets better when engine is warm, it is likely intake manifold gasket leak (motivation: When engine warms up, metal and gasket are expanding and close down the leak). If it is the same on both cold and warm, it is likely a leak in a manifold or somewhere else.
As said, take a spray bottle full of water, run the engine and listen for it to start sucking the water in. In some cases, it might affect the idle as well when water gets into cylinders. One word of advice, if there is a severe leak somewhere, don't drop too much water, as you are risking flooding the engine and getting it hydrolocked (pro mechanics say that there is no risk of that, but I would be careful). Another way is to use propane, but it is a dangerous thing, so I don't recommend that way.
Click to expand...
Understood and thanks for your advises. Will post an update once I will run the vacuum test
 
igno said:
OK, assuming that throttle is nice and clean, judging from previous posts and butterfly is not sticking, I would again suggest a vacuum leak test. There are 2 rather different types of vacuum leak. If it is only misbehaving at cold and gets better when engine is warm, it is likely intake manifold gasket leak (motivation: When engine warms up, metal and gasket are expanding and close down the leak). If it is the same on both cold and warm, it is likely a leak in a manifold or somewhere else.
As said, take a spray bottle full of water, run the engine and listen for it to start sucking the water in. In some cases, it might affect the idle as well when water gets into cylinders. One word of advice, if there is a severe leak somewhere, don't drop too much water, as you are risking flooding the engine and getting it hydrolocked (pro mechanics say that there is no risk of that, but I would be careful). Another way is to use propane, but it is a dangerous thing, so I don't recommend that way.
Click to expand...

I and my mechanic tried this... no vacuum leaks at all. We tried with water, we tried with smoke machine...

But when mechanic tried these approaches he heard some bad noise coming from the timing belt section. When he removed cover he saw that the belt is not stretched tight. He tried to fix it with tension roller - and the roller was broken. We decided to change the whole timing belt kit + water pump (which was the original one, worked for 218K!!!) I read that sometimes similar symptoms are occured of the timing belt issue.
BUT not in my case :( Nothing is changed.

Probably the ECU need some time ...
 
sgorchichko said:
I and my mechanic tried this... no vacuum leaks at all. We tried with water, we tried with smoke machine...

But when mechanic tried these approaches he heard some bad noise coming from the timing belt section. When he removed cover he saw that the belt is not stretched tight. He tried to fix it with tension roller - and the roller was broken. We decided to change the whole timing belt kit + water pump (which was the original one, worked for 218K!!!) I read that sometimes similar symptoms are occured of the timing belt issue.
BUT not in my case :( Nothing is changed.

Probably the ECU need some time ...
Click to expand...

well, the lack of tension of the timing belt is quite unlikely to cause high RPM at idle. But it is always a good idea to replace it & pump every now and again ... What does TPS value read on OBD when this issue is happening? is the battery / generator combo good? When replacing throttle bodies, did you also try new TPS sensor? Could you summarize what was actually tested / done to the car during the whole period?
 
sgorchichko said:
I and my mechanic tried this... no vacuum leaks at all. We tried with water, we tried with smoke machine...

But when mechanic tried these approaches he heard some bad noise coming from the timing belt section. When he removed cover he saw that the belt is not stretched tight. He tried to fix it with tension roller - and the roller was broken. We decided to change the whole timing belt kit + water pump (which was the original one, worked for 218K!!!) I read that sometimes similar symptoms are occured of the timing belt issue.
BUT not in my case :( Nothing is changed.

Probably the ECU need some time ...
Click to expand...
One more thing, perhaps I've missed it, does the car have an air conditioning?
 
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