[Antoniogreens]

Hello I just had to do a head swap for my 2.4L turbocharged pt cruiser. New head with valves and springs, replaced oil pump, water pump, plugs and wires, coil pack and timing belt. Car say sat for a few months because the head got warped due to high temperature cause oil pump went out. Now that I have it running it has a surging idle that I can't figure out. All vacuum lines seem to be fine no cracks or wear. When I take the vacuum line off the brake booster the vacuum just surges instead of a steady sucking. Has anybody ran into this problem or might now of which route I should take now?

 

[ImperialCrown]

Welcome to Allpar. I would double-check the crank/cam timing marks. It's easy to be a tooth off. Use a straight-edge across the sprocket bolt centers and a dental mirror to get a head-on view of the cam sprocket timing marks.
The marks must be dead-nuts aligned.
It is good practice to roll the engine crankshaft 2 complete turns after getting the belt on to get it centered and settled-in on the sprockets.

 

[Antoniogreens]

I put piston #1 at TDC made sure the intake valves were open and cam timing marks were on point when installed the new belt. I rotated the the crank 4 times and every 2 turns the cam timing marks matched up.

 

[ImperialCrown]

Sometimes the spark plug tips tell a story about combustion and mixture. Remove them and keep them in order to which cylinder they came out of. Look for any carbon fouling or other irregularities between cylinders. Are they the recommended Champion or NGK type for the car? The throttle body blade and bore clean?
Even compression in all cylinders?
What year PT?
Have you taken it for a good drive and the problem is only at idle? Any pending (one trip failures) or matured fault codes?

 

[Antoniogreens]

I haven't taken it any further than around the corner but the throttle lags until I reach up to 1800rpms, I'm guessing that's when its enough vacuum to operate properly. I replaced the spark plugs with copper champions, replaced wires and coil pack when I did the top end. Throttle body is clean tps sensor and map sensor are fine. But when I disconnect the PCV line from the manifold it seems to run a little better.

 

[Antoniogreens]

I have yet to check compression though I just turned the motor over yesterday no codes just a rough idle like it's not getting enough vacuum

 

[pt006]

I put piston #1 at TDC made sure the intake valves were open and cam timing marks were on point when installed the new belt. I rotated the the crank 4 times and every 2 turns the cam timing marks matched up.

#1 piston is the one closest to the timing belt. The TDC for the engine is when ALL valves are closed. A picture of the correct timing marks is posted on PT Cruiser > page 4 > PT Cruiser timing belt > post 2. Thanks to Imperial Crown.

 

[Bob Lincoln]

Cars don't 'get vacuum', they produce it. And the vacuum should be higher at idle than at 1800 RPM.

 

[Antoniogreens]

I know the car produces vacuum and that it doesn't just come out of nowhere. And I'm aware it should be higher at idle that's why I came to this forum for advice not to be talked down to.

 

[Antoniogreens]

I've been under the hood since I was in diapers and never ran into this problem thought I'd get more insight from other mechanics guess this forum is just for old guys to belittle people who run into problems instead of actually helping.

 

[Bob Lincoln]

Wow. No belittling was meant. And if I were that sensitive, I might take offense at the 'old guys' remark.

Just trying to steer you in the right direction. As in, turning up the idle would not help fix the underlying problem.

If it was OK before the head work, I would suggest something did not get assembled correctly. Maybe there is a vacuum leak at the intake manifold.

 

[Antoniogreens]

I replaced the head because it got warped. And I know you can't adjust the idle it's all controlled by the computer. I'm looking for a little advice before I take the head out to investigate. Maybe a leak between the intake/exhaust inside the head or something that's impairing it to run right ergo not being able to build negative pressure.

 

[djsamuel]

Just throwing this out there, but before tearing into too much, check the seals at the upper intake manifold where it joins the lower intake. If one of the seals shifted when installing the upper manifold you may have an issue there. That may not be the cause the surging, but worth looking at since it is simple to check.

 

[Antoniogreens]

I'll check it out thank you

 

[ImperialCrown]

A spray bottle of water around the seams might cause a 'reaction' or change in speed if there is a vacuum leak. A vacuum leak will usually cause a fast idle, like unplugging a hose on a running engine.

 

[Antoniogreens]

I've already sprayed everything down with carb cleaner and got to change in idle. My problem is a surging idle. But when I take the hose off the PCV valve it seems to run a little better but the chug is still there.

 

[Crawdaddy]

It is easy to get the exhaust one tooth off on these engines. They will look lined up! Count the number of teeth between the marks on the intake and exhaust cams using the belt. It should be an even number, if not the intake and exhaust cams are not in sync. It will not set a DTC because the cam sensor is on the intake cam. Nothing monitors the exhaust cam. It will cause the symptoms you are having.

 

[djsamuel]

Could the Idle Air Control valve be screwed up? Make sure the connector is firmly in place. I had a surging idle recently and replaced the IAC valve and it solved the issue.

 

[Antoniogreens]

@Crawdaddy that's what I am thinking I was pretty sure I had the cam marks 100% but I'm going to dig into it this weekend and see because every sensor and vacuum line is good so my next thing is to go back to timing or maybe there's a leak between the valves inside the head..