Check the many on-line parts sources;such as www.RockAuto.com, www.autopartswarehouse.com, or www.autopartsfair.com. For example, they (RockAuto) list the valve cover gasket set (including grommets and seals) from around $18.00, the oil pan gasket from around $13.00, and the front crank seal from around $4.00 for your vehicle.
Of course, these are only the parts prices - inexpensive when compared to the labor to install - the labor will be much more - figure on 2 to 4 hours for these items labor cost. The individual repair shop per hour charge can vary by location and by shop; from $55.00 / hour to around $100.00 / hour. The valve cover gasket is fairly simple to replace - this is one item even a novice do-it-yourself mechanic can tackle - to save some of the costs.

You need to add one more thing to your list of repairs. I would have the PCV valve checked. It sounds like pressure is building inside your engine and causing it to blow gaskets and seals. Should be a cheap part and you can install it yourself.

First step - have the check engine light or stored fault codes scanned - for free - at any local auto parts store; Advance Auto, Auto Zone, NAPA. Then, post a reply as 'add answer' for more assistance.

Possible Causes of Engine Hesitation or Stumble:

Dirty fuel injectors (cleaning the injectors often fixes this)
Dirty air filter (change filter)
Dirty / clogged fuel filter (change filter)
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires

I brought it to the auto parts store and they read the codes. They were signifying misfires. I then went to the repair shop and had a tune up. Some of the plugs were bad. After that everything works fine.

Sorry for the sudden failure. The choices are pretty straightforward; replace / rebuild the engine, replace the vehicle. The rebuilt / remanufactured engine (long block; consisting of engine block, cylinder head and few components) would cost around $1800.00 - $2000.00 - before the labor charge to replace - figure around another $500.00 to $750.00 in addition to the engine cost.
There is another alternative to consider; a used engine - from the many used engine sources - such as www.theautochannel.com/autoparts/used-enginespartshonda/civicitems.html

These are less expensive; around $1000.00 on up - and come with at least a 1 year warranty - some with 3 year warranties. Of course, you would still have to install the engine - but if it were my vehicle, and based on the overall condition, I'd give this option some consideration.

Honda Civic is a great car and there is nothing wrong in fixing it. The cost to replace the engine will vary greatly depending on which method you choose. A used engine installed might cost $2000 installed and a completely remanufactured engine with warranty will cost you about $4000 installed. Expensive either way. Wow, 8 days after purchase, incredible. He did not do a good job rebuilding obviously.

P0411 = Secondary Air Injection System Incorrect Flow Detected

Potential causes of a P0411 code include:
Damaged or missing check valve
AIR (air injection reaction) pump intake port plugged/damaged
AIR pump clutch malfunction
Holes or damage to exhaust components

Possible Solutions:

If you have access to a scan tool, with KOEO (Key on engine off) command the AIR pump on. It should activate. If it doesn't, remove and inspect the AIR pump relay for discoloration/melting due to heat. Repair as necessary.

With the ignition on (engine off) check for battery voltage at the switched battery feed to the relay and the relay control circuit. If either of these isn't present, inspect circuit for blown fuse or open/short in the wiring. Repair cause of short and retest. If they are both present, jumper the battery feed to AIR pump feed circuit using a fused jumper. The pump should activate. If not, check for power and ground present at the AIR pump when jumpered. If there is no voltage/ground present at pump repair open in wiring harness. If voltage and ground is present, but pump still does not run, suspect a bad AIR pump. If after jumpering the AIR pump feed circuit the pump activates then the problem is likely the AIR pump relay. Replace and retest.

If the scan tool activates the AIR pump, with KOER (Key on engine running) activate the AIR pump solenoid valve on and see if there is vacuum to the cutoff valve. It should have vacuum present to open the valve. If there is no vacuum present, check the AIR pump's vacuum solenoid valve for vacuum supply from the manifold. If there is vacuum present then the vacuum solenoid is likely bad. Replace it. If there is no vacuum present at the supply to the vacuum solenoid, check for a plugged or damaged vacuum line or plugged vacuum port. But if there is vacuum present at the cut-off valve, shut the engine off and using a vacuum pump, apply vacuum to the cut-off valve and see if it holds a vacuum and that air flows through it when vacuum is applied. If it doesn't hold vacuum or the valve doesn't flow when vacuum is applied, replace the cut-off valve. If the cut-off valve works properly, inspect the check valve for obstruction or to see if it's missing. Replace as necessary.

Check the steel line to the exhaust catalyst as well as the exhaust ports for damage or holes that could give a false reading.

P0411 is not a valid code for a '98 Honda Passport according to Alldata. The code is a real code yes, just not applicable to a "98 Passport. Maybe you were given the incorrect code by the person who checked it or you maybe read it incorrectly?

Careucar prompt: P0411 Secondary Air Injection System Incorrect Flow Detected, first you can try to erase the fault code with your obd2 scanner and observe a period of time, if it come again, you must repair it.

Careucar prompt: if it is the gas guage thats bad... try using a dust blower can on it(keyboard air duster), sometimes it is just dirty.

Please detail the stalling further. Not enough to go on. Tell the story and symptoms in detail.

I suspect that the timing belt has jumped a few teeth or has broken. If this engine has 100k or more on it the timing belt should have been replaced already. But, no matter, check the belt lineup.

Hello
What "stuff" over the counter did you use? Did you disturb any connections at the distributor when you where messing around with the thermostat?
Joe Boulay
Automotive Technician & Author
joe@joeboulay.com
www.joeboulay.com

110k or 84 mths is the recommended service interval. If you replaced it at 90, you have 118k on it. Since your vehicle has an interference engine, don't wait.

Depends on how many additional parts you add - like water pump, tensioner, seals, drive belts. $300 to $500. No timing adjustment.

Check the many on-line parts sources;such as www.RockAuto.com, www.autopartswarehouse.com, or www.autopartsfair.com. For example, they (RockAuto) list the timing component kit from around $64.00 for your vehicle. The kit includes;timing belt, belt tensioner, water pump, gasket and few other components

It could be coming from a leaking transmission cooler.